Illuminating system

ABSTRACT

The illuminating system comprises a linear light source, and a light guide member with the light source placed beside a side face thereof, in which the top face and the bottom face of the light guide member are generally parallel to each other and in which slits made of a different material or air are arranged at specified intervals in the top face of the light guide member. Therefore, most of light propagating within the light guide member is totally reflected at the slits formed in the light guide member so as to be outputted from the light guide member, thereby illuminating a reflecting plate. Its reflected light is incident again on the light guide member and the resulting totally reflected light is transmitted to the observer&#39;s side at places other than the slits, while the observer&#39;s field of view is not obstructed at the slit portions.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an illuminating system to beused for printed articles such as books and photographs, screen displaysof personal computers or other office automation equipment, portableinformation terminals, portable video tape recorders and the like, orreflection type liquid crystal displays used in various monitors, andthe like.

[0002] In recent years, personal computers, portable informationterminals, video tape recorders and the like have been becomingincreasingly small-sized and portable, making it an important issue toreduce the power consumption of their image display units. On thisaccount, many of them have been provided with reflection type liquidcrystal displays used as their image display units.

[0003] The reflection type liquid crystal display device is given screenbrightness by reflecting outside light such as sunlight and indoorlight. However, at places of less outside light, the device could notafford enough brightness in the screen. As a result of this, there havebeen invented several reflection type liquid crystal displays equippedwith an illuminating system which enables screen display even at placesof insufficient outside light.

[0004] An example of the illuminating system to be mounted on thereflection type liquid crystal display device is shown. FIG. 16 is aschematic cross-sectional view of a conventional illuminating system. Asshown in FIG. 16, the conventional illuminating system comprises a lightsource 1, a reflector 2, a light guide member 63 and a compensatingplate 5. In order that the reflector 2 collimates the light emitted fromthe light source 1, the distance from the light source 1 to a side faceof the light guide member 63 is elongated. The light guide member 63 hasa function of propagating the light introduced from the reflector 2 bytotally reflecting the light, and a function of illuminating areflecting plate 4 by totally reflecting the light with slopes ofgrooves formed in its top face to change the angle of the light. Thecompensating plate 5 has a function of correcting any distortion thatoccurs when the reflected light from the reflecting plate 4 passes thelight guide member 63.

[0005] However, in the conventional illuminating system, when the lightthat has been transmitted by the light guide member 63 to thecompensating plate 5 comes incident on the light guide member 63 againafter being totally reflected by the top face of the compensating plate5, part of the light is reflected by the slopes of the grooves of thetop face of the light guide member 63 so that groove lines are morevisible, as an issue. Also, whereas light is collimated by a reflectorto reduce the issue of these groove lines' visibility, the collimatedlight is more likely to reach one side of the light guide member 63opposite to the light source without impinging on the slopes of thegrooves of the light guide member 63. This would result in a lowilluminating efficiency, as another issue.

SUMMARY OF THE INVENTION

[0006] Therefore, an object of the present invention is to provide anilluminating system which makes groove lines less visible, maintains animage of reflected light successful and offers a good illuminatingefficiency.

[0007] In accomplishing these and other aspects, according to a firstaspect of the present invention, there is provided an illuminatingsystem comprising:

[0008] a light source; and

[0009] a transparent plate with the light source placed beside a sideface thereof,

[0010] wherein a plurality of grooves filled with a layer having arefractive index different from a refractive index of the transparentplate are arranged at specified intervals in a surface or interior ofthe transparent plate.

[0011] According to a second aspect of the present invention, there isprovided an illuminating system according to the first aspect, wherein atop face and a bottom face of the transparent plate are generallyparallel to each other.

[0012] According to a third aspect of the present invention, there isprovided an illuminating system according to the first or second aspect,wherein a condition of

θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)}

[0013] is satisfied where n is the refractive index of the transparentplate, n₁ is the refractive index of a material as the layer that fillsthe grooves which are the slits, θ is an angle formed by each of theslits and the top face of the transparent plate and β is an angle ofvisibility of the illuminating system.

[0014] According to a fourth aspect of the present invention, there isprovided an illuminating system comprising:

[0015] a light source;

[0016] a transparent first plate with the light source placed beside aside face thereof; and

[0017] a transparent second plate placed on a top face of the firstplate, wherein a bottom face of the first plate is a plane surface and aplurality of stepwise slopes are arranged at specified intervals in thetop face of the first plate;

[0018] in a bottom face of the second plate, stepwise slopes arearranged so as to be identical in configuration to the slopes of the topface of the first plate; and

[0019] the top face of the first plate and the bottom face of the secondplate are placed with a specified spacing.

[0020] According to a fifth aspect of the present invention, there isprovided an illuminating system according to the fourth aspect, whereina condition of

θ<sin⁻¹(n ₂ /n)−sin⁻¹{(1/n)sin(β)}

[0021] is satisfied where n is the refractive index of the first plate,n₂ is the refractive index of a material as the layer bonding the firstplate and the second plate to each other, θ is an angle of each of theslopes of the top face of the first plate and the bottom face of thesecond plate and β is an angle of visibility of the illuminating system.

[0022] According to a sixth aspect of the present invention, there isprovided an illuminating system according to the fifth aspect, wherein alight outgoing angle of a collimator placed at an outgoing exit of thelight source is within ±sin⁻¹[n×sin{90−θ−sin⁻¹(n₂/n)}].

[0023] According to a seventh aspect of the present invention, there isprovided an illuminating system by overhead irradiation comprising:

[0024] a light source;

[0025] a transparent plate which is a light guide member in which aplurality of grooves are arranged in a top face of the light guidemember at specified intervals in a direction parallel to a longitudinaldirection of the light source, and in which a flat portion constitutinga part of the top face is arranged between adjacent ones of the grooves,wherein an illumination object placed on a bottom face side of the lightguide member is observed from a top face side of the light guide member.

[0026] According to an eighth aspect of the present invention, there isprovided an illuminating system by overhead irradiation according to theseventh aspect, wherein each of the grooves of the light guide member isa V-shaped groove having a first slope located on one side closer to thelight source and a second slope located on the other side farther fromthe light source, and wherein an angle θ₁ formed by the first slope andthe bottom face of the light guide member falls within a range ofθ₁≦90°−θ_(c)+2θ₃, where θ_(c) is a total reflection angle of the lightguide member and θ₃ is an angle formed by the flat portion and thebottom face of the light guide member.

[0027] According to a ninth aspect of the present invention, there isprovided an illuminating system by overhead irradiation according to theseventh or eighth aspect, wherein each of the grooves of the light guidemember is a V-shaped groove having a first slope located on one sidecloser to the light source and a second slope located on the other sidefarther from the light source, and wherein an angle θ₁ formed by thefirst slope and the bottom face of the light guide member satisfies acondition of:

[0028] θ₁≈45+θ₃−(½)sin ⁻¹(1/n×sinβ), where n is a refractive index ofthe light guide member, θ₃ is an angle formed by the flat portion andthe bottom face of the light guide member and β is an angle formed by aperpendicular of the bottom face of the light guide member and adirection of the observer.

[0029] According to a tenth aspect of the present invention, there isprovided an illuminating system by overhead irradiation according to anyone of the seventh to ninth aspects, wherein each of the grooves of thelight guide member is a V-shaped groove having a first slope located onone side closer to the light source and a second slope located on theother side farther from the light source, and wherein an angle θ₂ formedby the second slope and the bottom face of the light guide membersatisfies a condition of θ₂≦(½)sin⁻¹(1/n), where n is a refractive indexof the light guide member.

[0030] According to an eleventh aspect of the present invention, thereis provided an illuminating system by overhead irradiation according toany one of the seventh to tenth aspects, wherein in the light guidemember, a pitch of the grooves is not more than a dot pitch of theillumination object.

[0031] According to a twelfth aspect of the present invention, there isprovided an illuminating system by overhead irradiation according to anyone of the seventh to eleventh aspects, wherein each of the grooves ofthe light guide member is a V-shaped groove having a first slope locatedon one side closer to the light source and a second slope located on theother side farther from the light source, and wherein in the light guidemember, a length of the first slope is not more than{L×(0.5/60)×_(π+B/180)}, where L is a distance between the top face ofthe light guide member and an observer observing the illuminationobject.

[0032] According to a thirteenth aspect of the present invention, thereis provided an illuminating system by overhead irradiation according toany one of the seventh to twelfth aspects, wherein a transparent prismsheet is placed on the top face of the light guide member, the prismsheet having, with respect to a cross-sectional shape, a plurality ofprojected portions having slopes of an angle θ₄ to the top face arearranged on the bottom face so that a flat portion generally parallel tothe bottom face is interposed therebetween.

[0033] According to a fourteenth aspect of the present invention, thereis provided an illuminating system by overhead irradiation according tothe thirteenth aspect, wherein the length of the slope of the prismsheet is not more than {L×(0.5/60)×_(π)/180}, where L is the distancebetween the observer who observes the illumination object and the topface of the light guide member.

[0034] According to a fifteenth aspect of the present invention, thereis provided an illuminating system comprising:

[0035] a light source; and

[0036] a transparent plate taking light from the light source through aside face thereof and projecting illumination light through a lower facethereof subjected to at least one of an anti-reflection treatment and adiffuse treatment,

[0037] wherein an illumination object which is disposed at a lower faceside of the transparent plate is observed from an upper face side of thetransparent plate.

[0038] According to a sixteenth aspect of the present invention, thereis provided a reflection type liquid crystal display device whichcomprises:

[0039] the illuminating system according to the first aspect, thetransparent plate taking light from the light source through a side facethereof and projecting illumination light through a lower face thereofsubjected to at least one of an antireflection treatment and a diffusetreatment; and

[0040] a reflection type liquid crystal panel having a surface of atleast one substrate thereof processed through at least one of theanti-reflection treatment and the diffuse treatment,

[0041] wherein the surface of the substrate of the liquid crystal panelprocessed through at least one of the anti-reflection treatment and thediffuse treatment is arranged to confront a lower face of thetransparent plate, so that the reflection type liquid crystal panel isobserved from an upper face side of the transparent plate.

[0042] According to a seventeenth aspect of the present invention, thereis provided a reflection type liquid crystal display device whichcomprises:

[0043] the illuminating system according to the first aspect, thetransparent plate taking light from the light source through a side facethereof and projecting illumination light through a lower face thereofsubjected to at least one of an antireflection treatment and a diffusetreatment;

[0044] a reflection type liquid crystal panel having a surface of atleast one substrate thereof processed through at least either ananti-reflection treatment or a diffuse treatment; and

[0045] a touch panel having a surface processed through a diffusetreatment,

[0046] wherein the surface of the substrate of the liquid crystal panelprocessed through at least either the anti-reflection treatment or thediffuse treatment is arranged to confront the lower face of thetransparent plate and at the same time, the touch panel is disposed toconfront an upper face of the transparent plate, so that the reflectiontype liquid crystal panel is observed from an upper face side of thetransparent plate.

[0047] According to an eighteenth aspect of the present invention, thereis provided a reflection type liquid crystal display device according toany one of the sixteenth to seventeenth aspects, wherein a haze value ofthe diffuse treatment provided to the surface of the substrate of thereflection type liquid crystal panel, the lower face of the transparentplate or the surface of the touch panel is set to be not larger than20%.

[0048] According to a nineteenth aspect of the present invention, thereis provided a reflection type liquid crystal display device according toany one of the sixteenth to eighteenth aspects, wherein a transparentmaterial or a sheet of the material which has approximately the samerefractive index as that of a material of the transparent plate and thatof the substrate of the reflection type liquid crystal panel isinterposed between the lower face of the transparent plate and thereflection type liquid crystal panel.

[0049] According to a 20th aspect of the present invention, there isprovided a reflection type liquid crystal display device whichcomprises:

[0050] the illuminating system according to the first aspect, thetransparent plate taking light from the light source through a side facethereof and projecting illumination light from a lower face thereof; and

[0051] a reflection type liquid crystal panel having an field anglecontrol plate arranged on an upper face thereof, said control platefeaturing a diffuse characteristic in one direction while beingtransparent in other directions,

[0052] wherein the face of the reflection type liquid crystal panelwhere the field angle control plate is arranged is set to confront thelower face of the transparent plate, and moreover an angle of theillumination light projected from the lower face of the transparentplate is almost agreed with a diffusion direction of the field anglecontrol plate, so that the reflection type liquid crystal panel isobserved from an upper face side of the transparent plate.

[0053] According to a 21st aspect of the present invention, there isprovided a reflection type liquid crystal display device according tothe 20th aspect, wherein an output angle of the transparent plate andthe diffusion direction of the field angle control plate is 30-50° to anormal direction of the reflection type liquid crystal panel.

[0054] According to a 22nd aspect of the present invention, there isprovided an illuminating system according to the first aspect, whereinthe light house is a group of point light sources in which point lightsources are arranged on an almost straight line via a constant intervalto radiate in nearly the same direction,

[0055] the illuminating system further comprising:

[0056] a reflector having an opening part and disposed to cover thegroup of point light sources; and

[0057] a diffusing plate set at the opening part of the reflector,

[0058] wherein the diffusing plate is separated from the group of pointlight sources so that quantity of light from a center of an illuminancedistribution by the point light source on the diffusing plate is nearlyequal to that between centers of illuminance distributions of the pointlight sources.

[0059] According to a 23rd aspect of the present invention, there isprovided an illuminating system according to the 22nd aspect, whereinthe reflector is L-shaped so as not to directly pass light emitted fromthe point light sources to the diffusing plate.

[0060] According to a 24th aspect of the present invention, there isprovided an illuminating system according to the 22nd aspect, whichfurther comprises a light guide member which outputs light entering froma side face thereof after emitted from the diffusing plate arranged atthe opening part of the reflector of the linear light source, from alower face side thereof by grooves formed in a lower face or an upperface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] These and other aspects and features of the present inventionwill become clear from the following description taken in conjunctionwith the preferred embodiments thereof with reference to theaccompanying drawings, in which:

[0062]FIG. 1 is a schematic view of a cross section of an illuminatingsystem according to a first embodiment of the present invention;

[0063]FIG. 2 is a schematic view showing an arrangement of slits in thefirst embodiment;

[0064]FIG. 3 is a view for explaining the propagation of light withinthe light guide member in the first embodiment;

[0065]FIG. 4 is a view for explaining the propagation of reflected lightwithin the light guide member in the first embodiment;

[0066]FIG. 5 is a schematic view of a cross section of an illuminatingsystem according to a second embodiment of the present invention;

[0067]FIG. 6 is a view for explaining the propagation of light withinthe light guide member in the second embodiment;

[0068]FIG. 7 is a view for explaining the propagation of light withinthe light guide member in the second embodiment;

[0069]FIG. 8 is a view for explaining the propagation of reflected lightwithin the light guide member in the second embodiment;

[0070]FIGS. 9A and 9B are a schematic sectional view and a plan view ofthe collimator in the second embodiment;

[0071]FIG. 10 is a view for explaining operation of the collimator inthe second embodiment;

[0072]FIG. 11 is a schematic view of a cross section of a modificationof the illuminating system of the first embodiment of the invention;

[0073]FIG. 12 is a schematic view of a cross section of anothermodification of the illuminating system of the first embodiment of theinvention;

[0074]FIG. 13 is a schematic view of a cross section of still anothermodification of the illuminating system of the first embodiment of theinvention;

[0075]FIG. 14 is a schematic view of a cross section of an example ofthe illuminating system of the second embodiment of the invention;

[0076]FIGS. 15A and 15B are a schematic sectional side view and a planview of the collimator of the illuminating system in the thirdembodiment;

[0077]FIG. 16 is a schematic view of a cross section of an illuminatingsystem according to the prior art;

[0078]FIG. 17 is a schematic view of a cross section of a modificationof the illuminating system of the second embodiment of the invention;and

[0079]FIG. 18 is a schematic view of a cross section of anothermodification of the illuminating system of the second embodiment of theinvention;

[0080]FIG. 19 is a schematic view of the illuminating system by overheadirradiation according to a third embodiment of the present invention;

[0081]FIG. 20 is a cross-sectional schematic view of the light guidemember in the third embodiment;

[0082]FIG. 21 is a cross-sectional schematic view showing in detail thegroove in the third embodiment;

[0083]FIGS. 22A, 22B, 22C, 22D, 22E are views for explaining thereflection of light at the top face of the light guide member in thethird embodiment;

[0084]FIGS. 23A, 23B, 23C are cross-sectional schematic views showinganother example of the illuminating system in the third embodiment;

[0085]FIG. 24 is a cross-sectional schematic view of an illuminatingsystem by overhead irradiation according to a fourth embodiment of thepresent invention;

[0086]FIG. 25 is a cross-sectional schematic view of the prism sheet inthe fourth embodiment;

[0087]FIG. 26 is a graph showing the radiation distribution of lightoutputted from the top face of the light guide member in the fourthembodiment;

[0088]FIG. 27 is a view for explaining the reflection of light at prismportions in the fourth embodiment;

[0089]FIGS. 28A, 28B are cross-sectional schematic views showing anotherexample of prism sheet in the fourth embodiment;

[0090]FIG. 29 is a view for explaining the propagation of light withinthe prism sheet in the fourth embodiment;

[0091]FIG. 30 is a view of an illuminating system by overheadirradiation in a fifth embodiment of the present invention, as viewedfrom the top;

[0092]FIG. 31 is a cross-sectional schematic view of the light guidemember in the fifth embodiment;

[0093]FIG. 32 is a more detailed cross-sectional schematic view of theilluminating system by overhead irradiation in the third embodiment;

[0094]FIG. 33 is a more detailed cross-sectional schematic view of theilluminating system by overhead irradiation in the fourth embodiment;

[0095]FIG. 34 is a more detailed cross-sectional schematic view of theilluminating system by overhead irradiation in the fourth embodiment;

[0096]FIG. 35 is a cross-sectional schematic view of an illuminatingsystem according to the prior art;

[0097]FIG. 36 is a schematically sectional view of an illuminatingsystem according to a seventh embodiment of the present invention;

[0098]FIG. 37 is a schematically sectional view of a transparent plateof the seventh embodiment of the present invention;

[0099]FIG. 38 is a schematically sectional view of a reflection typeliquid crystal display device according to the seventh embodiment of thepresent invention;

[0100]FIG. 39 is a schematically sectional view of a reflection typeliquid crystal display device according to an eighth embodiment of thepresent invention;

[0101]FIG. 40 is a diagram explanatory of the seventh embodiment of amethod for manufacturing the transparent plate;

[0102]FIG. 41 is a diagram showing how the transparent plate is held inthe manufacture method of FIG. 40;

[0103]FIG. 42 is a schematically sectional view of a reflection typeliquid crystal display device in a ninth embodiment of the presentinvention;

[0104]FIG. 43 is a diagram explanatory of the propagation;

[0105]FIG. 44 is a schematically sectional view of an illuminatingsystem of a tenth embodiment of the present invention;

[0106]FIG. 45 is a plan view of the illuminating system of FIG. 44;

[0107]FIG. 46 is a perspective view of a light guide member and areflecting plate of the illuminating system of FIG. 44;

[0108]FIG. 47 is an enlarged view of a circular part of FIG. 46; and

[0109]FIGS. 48 and 49 are explanatory views of distance selectionbetween light sources and a diffusing plate of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0110] Before the description of the present invention proceeds, it isto be noted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

[0111] Hereinbelow, an illuminating system according to a firstembodiment of the present invention is described with reference to theaccompanying drawings.

[0112]FIG. 1 shows a schematic view of a cross section of theilluminating system in the first embodiment of the invention withouthatching in order to clearly show the lines. In the illuminating systemof the first embodiment of the invention, an angle at which an observerviews the illuminating system from above (hereinafter, referred to as anangle of visibility (field angle)) is assumed to be β.

[0113] Referring to FIG. 1, reference numeral 1 denotes a light source,in which, for example, fluorescent lamps, such as hot cathode-ray tubesor cold cathode-ray tubes, or light emitting diodes are arrayed in alinear shape, or in which incandescent lamps or organic light-emittingmaterials are formed into a linear shape. The light source 1 is arrangedon one side of a light guide member 3.

[0114] In FIG. 1, reference numeral 2 denotes a reflector, which isplaced so as to cover the light source 1, and of which the inner surfaceis so made as to have a high reflectance and a small diffusivity. Forexample, the reflector is made up by depositing a high-reflectancematerial such as silver or aluminum on a resin sheet, and bonding thissheet to a thin metal plate or resin sheet. When the light source 1 isfluorescent lamp(s), it is desirable to fill the gap between the lightsource 1 and the reflector 2 with a material having a refractive indexclose to the glass' refractive index of 1.5. It is also desirable thatthe thickness of one side face of the light guide member 3 on the lightsource 1 side and the height of the reflector 2 are equal to each other.The reason of this is that whereas the light guide member 3 is desirablythinner than not, the lower limit value of the thickness is the heightof the reflector 2 because of the incidence efficiency.

[0115] In FIG. 1, reference numeral 3 denotes a transparent plate(hereinafter, referred to as light guide member), which is made from amaterial such as quartz, glass, transparent resin like acrylic resin orpolycarbonate, or the like. Top face and bottom face of the light guidemember 3 are generally parallel to each other, and the light guidemember 3 is generally rectangular shaped as viewed from top. Side faceand top face as well as side face and bottom face of the light guidemember 3 each form an angle of nearly 90 degrees. Slits 31 as groovesare formed in the bottom face of the light guide member 3.

[0116]FIG. 2 shows a detailed view of a portion of the slits 31. Theslits 31 extend generally parallel longitudinally of the light source 1.Each slit 31 is internally filled with a material of low refractiveindex, which is exemplified by air or fluorine-contained resin. Further,the slit 31 satisfies the following condition:

θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)}

[0117] where n is the refractive index of the light guide member, n₁ isthe refractive index of the slit interior, θ is the angle formed by theslit 31 and the top face of the light guide member and β is the angle ofvisibility.

[0118] In the first embodiment, the material of the light guide memberis PMMA (polymethylmethacrylate), the slit interior is air and the angleof visibility is 40 degrees. Therefore, from n=1.5, n₁=1 and β=40, anangle θ formed by the slit 31 and the top face of the light guide memberhas been set to 16 degrees. Besides, a length 33 of the slit 31 is 50μm, and a pitch 32 of the slits 31 is 200 μm. If the angle of visibilityβ=30, then θ=22.34°.

[0119] In FIG. 1, reference numeral 4 denotes a reflecting plate. Thereflecting plate 4 means a printed article such as a book or photograph,a screen display unit of personal computers or other office automationequipment, portable information terminals, portable video tape recordersand the like, or a reflection type liquid crystal display used invarious monitors.

[0120] Next, propagation of light within the light guide member 3 isdescribed with reference to FIG. 3.

[0121] Light incident on the light guide member 3 results in lighthaving a radiation distribution of ±sin⁻¹(1/n) according to Snell's law,given that the refractive index of the light guide member 3 is n. Sincemost of the above-mentioned materials of the light guide member 3 have arefractive index of not less than 1.42, the radiation distribution fallswithin a range of ±44.77 degrees. In the light guide member 3, its topface and bottom face are generally parallel to each other, and its sideface and top face as well as its side face and bottom face, the sideface being planes of incidence on the light guide member 3, form anangle of nearly 90° C., respectively. Therefore, when light incident ona side face of the light guide member 3 comes incident on its top faceor bottom face, the minimum value of incident angle is 90−44.77=45.23degrees. With a refractive index of not less than 1.42, because theangle of total reflection is 44.77 degrees or lower, light incident onthe side face is totally reflected by the top face and the bottom face.

[0122] At places other than near the slits 31, light that propagatesthrough the light guide member 3 is totally reflected by flat portionsof the top face and the bottom face of the light guide member 3. At theportions of the slits 31, the light is separated into transmitted beamsof light and totally reflected beams of light depending on the angle oflight. As shown in FIG. 3, on the assumption that the angle formed by alight beam and the top face of the light guide member 3 is α, if

α>90−θ−sin⁻¹(n ₁ /n),

[0123] then the light is transmitted through the slits 31; and if

α<90−θ−sin⁻¹(n ₁ /n),

[0124] then the light is totally reflected by the slits 31.

[0125] A beam of light transmitted through the slits 31 is totallyreflected by the flat portion of the top face of the light guide member3, thus propagating again. The beam of light totally reflected by theslit 31 goes out from the bottom face of the light guide member 3, wherethe angle of incidence on the bottom face is {90 −(2η+α)} and fromSnell's law, if

90−(2η+α)<sin⁻¹(1/n),

[0126] then the light beam goes out from the bottom face of the lightguide member 3, thus illuminating the reflecting plate 4.

[0127] In this way, the illuminating system of the first embodimentilluminates the reflecting plate 4. Because the light emitted from thelight source 1 does not need to be collimated, the light is totallyreflected by the slits 31 at a high rate, so that the reflecting plate 4can be illuminated with high efficiency. Also, the light transmittedthrough the slits 31 propagates once again through the light guidemember 3, producing an effect that the groove lines are less visible.

[0128] Next, propagation of the reflected light that has illuminated thereflecting plate 4 is described with reference to FIG. 4. Lightoutputted for illumination from the light guide member 3 illuminates thereflecting plate 4, and turns back as reflected light. The reflectedlight comes incident again on the light guide member 3 from its bottomface, and is outputted from the top face of the light guide member 3 asit is at portions other than near the slits 31.

[0129] Near the slits 31, if the angle of incidence of the reflectedlight on the bottom face of the light guide member 3 is γ, then

θ+sin⁻¹{(1/n)sin(γ)}>sin⁻¹(n ₁ /n),

[0130] the light is totally reflected by the slits 31. On this account,upon incidence of the reflected light 41 on the bottom face of the lightguide member 3 at an angle γ, if γ >β, then the reflected light 41 istotally reflected by the slits 31, not reaching the observer; if γ≦β,then the reflected light 41 is transmitted through the slits 31,reaching the observer.

[0131] From this fact and another that the angle θ of the slits 31 is

θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)},

[0132] the reflected light is not totally reflected by the portions ofthe slits 31 in a range of the angle of visibility ±β. Thus, theobservers field of view is not obstructed, and a successful image can beobtained.

[0133] As shown above, according to this first embodiment, theilluminating system which makes the groove lines of the light guidemember 3 less visible, maintains an image of reflected light successfuland offers a good illuminating efficiency can be provided. Also, sinceuniform illumination is enabled and the light outputted from the lightsource 1 does not need to be collimated, the reflector 2 can be reducedin size. Moreover, since the height of the reflector 2 and the height ofthe side face of the light guide member 3 are made generally equal toeach other as described above, the thickness of the side face of thelight guide member 3 can be reduced according to the height of thereflector 2.

[0134] In addition, in the first embodiment, the slits 31 have beenarranged in the top face of the light guide member 3. However, it isalso possible that the slits 31 are arranged between the top face andthe bottom face of the light guide member 3 as shown in FIG. 11, or inthe bottom face of the light guide member 3 as shown in FIG. 12, orobliquely in a direction from the top face side to the bottom face sideof the light guide member 3 as shown in FIG. 13.

[0135] Further, although top face and bottom face of the light guidemember 3 are parallel to each other in the first embodiment, they may benon-parallel.

[0136] Furthermore, although the pitch 32 of the slits 31 has been madeto be a constant interval in the first embodiment, making the pitch 32decreasing with increasing distance from the light source 1 for thelight guide member 3 causes the brightness difference between nearplaces and far places from the light source 1 to be reduced, so thatmore uniform illumination can be obtained. Making the length 33 of theslits 31 increasing with increasing distance from the light source 1 forthe light guide member 3 also allows similar effects to be obtained.Still also, making the angle θ of the slits 31 increasing withincreasing distance from the light source 1 allows similar effects to beobtained.

[0137] Now, an illuminating system according to a second embodiment ofthe present invention is described below with reference to FIG. 5.

[0138]FIG. 5 is a schematic view of a cross section of the illuminatingsystem in the second embodiment of the invention. In the illuminatingsystem of the second embodiment of the invention, the angle ofvisibility is assumed as β.

[0139] In FIG. 5, the light source 1 and the reflector 2 are similar tothose of the first embodiment.

[0140] Referring to FIG. 5, reference numeral 30 denotes a light guidemember as an example of the first transparent plate, and 6 denotes acompensating plate as an example of the second transparent plate placedon the light guide member 30. Reference numeral 5 denotes a collimatorplaced between the light source 1 and the light guide member 30, and thecollimator 5 collimates light emitted from the light source 1. Outputcharacteristic of the collimator 5 is within±sin−¹[n×sin{90−θ−sin⁻¹(n₂/n)}], where θ is the angle of a stepwiseslope 131 of the top face of the light guide member 30, n is therefractive index of the light guide member 30 and n₂ is the refractiveindex of the material between the light guide member 30 and thecompensating plate 6.

[0141] For example, if β=40, n=1.5 and n₂=1, then θ=16°, where theoutput characteristic of the collimator 5 is ±52.13°. Also, if β=30,n=1.5 and n₂=1, then θ=22.34, where the output characteristic of thecollimator 5 is ±40.85°.

[0142] The structure of the collimator 5 can be implemented by, forexample, a plano-convex cylindrical lens satisfying the above outputcharacteristic. Further, the collimator 5 may also be a diffractiongrating. Besides, with a large angle of visibility β of the illuminatingsystem, the output characteristic angle of the collimator 5 is so largethat the collimator 5 may be omitted.

[0143] The light guide member 30 is made from a material such as quartz,glass, transparent resin like acrylic resin or polycarbonate, or thelike. FIG. 6 shows a detailed view of the light guide member 30. Abottom face of the light guide member 30 is a plane surface, and aplurality of stepwise slopes 131 are arranged at specified intervals inthe top face of the light guide member 30. The slopes 131 are generallyparallel to the longitudinal direction of the light source 1.

[0144] Assuming that the angle of each slope 131 is 0, the refractiveindex of the material of the light guide member 30 is n, the refractiveindex of the material between the light guide member 30 and thecompensating plate 6 is n₂ and that the angle of visibility is β, thenangle θ of the slope 131 is

θ<sin⁻¹(n ₂ /n)−sin⁻¹{(1/n)sin(β)}.

[0145] A pitch 32 of the slopes 131 is preferably decreasing withincreasing distance from the light source 1 for the light guide member30. Also, a length 33 of the slopes 131 may be increasing withincreasing distance from the light source 1 for the light guide member30. Further, the angle θ of the slopes 131 may be increasing withincreasing distance from the light source 1. The light guide member 30is generally rectangular shaped as viewed from top.

[0146] The compensating plate 6 is made from a material such as quartz,glass, transparent resin like acrylic resin or polycarbonate, or thelike. In the compensating plate 6, stepwise slopes 61 are arranged inits bottom face so as to be identical in configuration to the slopes 131of the top face of the light guide member 30, and the top face of thecompensating plate 6 is a plane surface. The top face of the light guidemember 30 and the bottom face of the light guide member 30 are placed ata specified spacing.

[0147] In FIG. 5, reference numeral 4 denotes a reflecting plate. Thereflecting plate 4 means a printed article such as a book or photograph,a screen display unit of personal computers or other office automationequipment, portable information terminals or portable video taperecorders, a reflection type liquid crystal display used in variousmonitors or the like.

[0148] Next, propagation of light within the light guide member 30 inthe second embodiment is described with reference to FIG. 7. Lightincident on the light guide member 30 propagates while being totallyreflected by flat portions of the top face or bottom face of the lightguide member 30 at places other than near the slopes 131 of the lightguide member 30. At the portions near the slopes 131 of the light guidemember 30, the light is separated into transmitted beams of light andtotally reflected beams of light depending on the angle of the light. Onthe assumption that the refractive index of the light guide member 30 isn, the refractive index of the material between the light guide member30 and the compensating plate 6 is n₂, the angle formed by the bottomface of the light guide member 30 and the light is α, and that the angleof the slopes 131 of the light guide member 30 is θ, if

α>90−θ−sin⁻¹(n ₂ /n)

[0149] then the light is transmitted through the slopes 131 of the lightguide member 30; and if

α<90−θ−sin⁻¹(n ₂ /n)

[0150] then the light is totally reflected by the slopes 131 of thelight guide member 30.

[0151] The light transmitted through the slopes 131 of the light guidemember 30 will not be reflected until it reaches one side of thecompensating plate 6 opposite to the light source 1 side. Therefore, thelight is highly likely to go out toward the observer's side, causing adeterioration of the illuminating efficiency. However, because theoutput characteristic of the collimator 5 for the light source 1 iswithin ±sin⁻¹[n×sin(90−θ−sin⁻¹{n₂/n)}], the light incident on the lightguide member 30 is within ±{90−θ−sin⁻¹(n₂/n)}, satisfying the conditionof Equation α<90−θ−sin⁻¹(n₂/n), so that most of the light is totallyreflected by the slopes 131 of the light guide member 30, illuminatingthe reflecting plate 4.

[0152] Therefore, the light emitted from the light source 1 is enabledto display the reflecting plate 4 with high efficiency. Also, since thereflecting plate 4 is illuminated with high efficiency in this way, lesslight is transmitted through the slopes 131 of the light guide member 30to the observer side, producing an effect that the groove lines are lessvisible.

[0153] Next, propagation of the reflected light that has illuminated thereflecting plate 4 is described with reference to FIG. 8. The light beamoutputted for illumination from the light guide member 30 illuminatesthe reflecting plate 4, and turns back as reflected light. The reflectedlight comes incident again on the light guide member 30 from its bottomface, and is outputted from the top face of the light guide member 30 asit is at portions other than near the slopes 131 of the light guidemember 30.

[0154] Near the slopes 131 of the light guide member 30, on theassumption that the angle of incidence of the reflected light on thebottom face of the light guide member 30 is γ, if

θ+sin⁻¹{(1/n)sin(γ)}>sin⁻¹(n ₂ /n),

[0155] then the light is totally reflected by the slopes 131 of thelight guide member 30. On this account, upon incidence of the reflectedlight 41 on the bottom face of the light guide member at an angle γ, ifγ>β, then the reflected light 41 is totally reflected by the slopes 131,not reaching the observer; if γ≦β, the reflected light 41 is transmittedthrough the slopes 131, reaching the observer.

[0156] From this fact and another that the angle θ of the slopes 131 ofthe light guide member 30 is

θ<sin⁻¹(n ₂ /n)−sin⁻¹{(1/n)sin(β)},

[0157] the reflected light is not totally reflected by the portions ofthe slopes 131 of the light guide member 30 in a range of the angle ofvisibility ±β. Thus, the observer's field of view is not obstructed, anda successful image can be obtained.

[0158] As shown above, according to the second embodiment, theilluminating system which makes groove lines of the light guide member30 less visible, maintains an image of reflected light successful andoffers a good illuminating efficiency can be provided.

[0159] In addition, although the groove has been formed stepwise in thesecond embodiment, the groove may also be an arbitrary curve as shown inFIG. 14. Further, although the pitch 32 of the slopes 131 has been aconstant interval in the second embodiment, making the pitch 32decreasing with increasing distance from the light source 1 for thelight guide member 30 causes the brightness difference between nearplaces and far places from the light source 1 to be reduced, so thatmore uniform illumination can be obtained. Making the length 33 of theslopes 131 increasing with increasing distance from the light source 1for the light guide member 30 also allows similar effects to beobtained. Still also, making the angle θ of the slopes 131 increasingwith increase distance from the light source 1 allows similar effects tobe obtained.

[0160] Also, even if the top face of the compensating plate 6 and thebottom face of the light guide member 30 are not parallel to each otheras shown in FIG. 17, similar effects can be obtained.

[0161] Also, even if the top face of the compensating plate 6 is acurved surface as shown in FIG. 18, similar effects can be obtained.

[0162] Now, an illuminating system according to a third embodiment ofthe present invention is described below.

[0163] The third embodiment of the invention is almost similar instructure to the second embodiment, and differs therefrom only in thestructure of the collimator 5.

[0164] The structure of the collimator 5 of the third embodiment isdescribed with reference to FIG. 9. A light incident surface 51 of thecollimator 5 is a plane surface. An output surface 52 of the collimator5 is so structured as to have a plurality of conical recessed portionswith apex angle 2δ.

[0165] On the assumption that the refractive index of the light guidemember 30 is n, the refractive index of the material bonding the lightguide member 30 and the compensating plate 6 to each other is n₂ and therefractive index of the collimator 5 is n₃, δ is a value that satisfiesthe equation:

sin⁻¹ [n×sin{90−θ−sin⁻¹(n ₂ /n)}]=90−δ−sin⁻¹ [n ₃×sin(90−δ−sin⁻¹(1/n₃)}].

[0166] Next, operation of the collimator 5 is described with referenceto FIG. 10. Light emitted from the light source 1, when incident on theincident surface 51 of the collimator 5, results in a radiationdistribution of ±sin⁻¹(1/n₃). Therefore, the angle of light incident onthe slopes 52 of the collimator 5 on its output side can be determinedgeometrically, where an incident-angle minimum value i_(min) is

i _(min)=90−δ−sin⁻¹(1/n ₃),

[0167] and the incident-angle maximum value i_(max) is

+I_(max)=90.

[0168] Also, the angle of light outputted from the collimator 5 can bedetermined by Snell's law, where an outgoing angle minimum value o_(min)with respect to the slope 52 on the outgoing side is

o _(min)=sin⁻¹ {n ₃×sin(i _(min))},

[0169] and an outgoing angle maximum value o_(max) is

o _(max)=90.

[0170] Because the slope 52 on the outgoing side is tilted by δ withrespect to the optical axis, an outgoing angle maximum value ω_(max) is

ω_(max)=90−δ−o _(min),

[0171] and the outgoing angle minimum value ω_(min) is

ω_(min)=−δ.

[0172] That is,

ω_(max)=90−δ−sin⁻¹ [n ₃×sin{90−δ−sin⁻¹(1/n ₃)}],

ω_(min)=−δ.

[0173] In this connection, if the angle of the slope 131 of the lightguide member 30 is θ and the refractive index of the material betweenthe light guide member 30 and the compensating plate 6 is n₂, thennecessary output characteristic of the collimator 5 is within±sin⁻¹[n×sin{90−θ−sin⁻¹(n₂/n))}]. Because δ is a value satisfying theequation, sin⁻¹[n×sin{90−θ−sin⁻¹(n₂/n)}]=90−δ−sin⁻¹[n₃×sin{90−δ−sin⁻¹(1/n₃)}], ω_(max)=(output characteristic ofcollimator 5), thus satisfying a desired output characteristic.

[0174] For example, if angle of visibility β=30, n=1.5, n₂=1 and n₃=1.5,then θ=22.4 so that the necessary output characteristic is 40.85°, wherewith δ=46.2°, the resulting outgoing angle is ω_(max)=+40.81° andω_(min)=46.2°, so that a desired output characteristic of the collimator5 is obtained. Also, if δ is a value satisfying an equation,δ=sin⁻¹[n×sin{90−θ−sin⁻¹(n₂/n)}], then, in the above example, δ=40.85°,ω_(max)=+38.10° and ω_(min)=40.85° so that a desired outputcharacteristic of the collimator 5 is obtained. In addition, under theabove conditions, δ may be an arbitrary value of not less than 40.85°and not more than 46.2°.

[0175] As shown above, with the use of the third embodiment, thecollimator 5 which satisfies the output characteristic necessary for thelight guide member 30 can be implemented and the same effects as in thesecond embodiment can be obtained.

[0176] In addition, the outgoing surface 52 of the collimator 5 has beenshaped into conical recessed portions with the apex angle 2δ in thethird embodiment. However, the outgoing surface 52 may also be shapedinto conical protrusions with the apex angle 2δ. Further, the outgoingsurface 52 may be shaped into polygonal pyramids having a cross sectionwith the apex angle 2δ instead of the conical shape. Still further, theoutgoing surface 52 may be shaped into parallel grooves with the acuteangle 2δ as shown in FIGS. 15A, 15B.

[0177] According to the present invention, light emitted from the lightsource becomes incident on the transparent plate, and propagates on andon while being iteratively totally reflected within the transparentplate. During this process, the light is separated into totallyreflected beams of light by the slits provided inside the transparentplate and transmitted beams of light depending on the angle of light.The totally reflected beams of light are changed in angle so as to besmaller than the total reflection angle, thus being outputted to thebottom face side of the transparent plate. Also, the transmitted beamsof light are totally reflected by the top face of the transparent plateso as to continuously propagate within the transparent plate, thusgroove lines of the transparent plate being less visible. Further, thelight is transmitted through the grooves and the collimator that hasconventionally been needed to make the groove lines less visible is nolonger needed, so that almost all the beams of light are outputted tothe bottom side of the transparent plate, thus offering a goodilluminating efficiency.

[0178] The light outgoing from the bottom face of the transparent plateilluminates an illumination object, and reflected light from theillumination object is made to be incident again on the transparentplate, where because

θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)},

[0179] a successful image can be displayed without being affected by theangle of visibility (field angle).

[0180] Thus, an illuminating system which makes groove lines lessvisible and has a good illuminating efficiency can be provided.

[0181] In other words, as described above, according to the presentinvention, a light source, for example a linear light source, is placedbeside a side face of a flat-shaped light guide member, and slits as anexample of grooves are arranged inside the light guide member so as toextend generally parallel to the light source, by which most of thelight that propagates within the light guide member can be outputtedfrom the light guide member by total reflection at the slits formed inthe light guide member so that a reflecting plate as an example of theillumination object can be illuminated. Also, because beams of lighttransmitted without being totally reflected by the slits propagate againwithin the light guide member, the groove lines are less visible, andbecause the reflected light from the reflecting plate is transmitted tothe observer side without being distorted, a successful image quality ofthe reflecting plate can be maintained. Further, because the lightemitted from the light source does not need to be collimated, theilluminating system can be downsized, and because all the beams of lightare outputted from the light guide member by the total reflection at theslits, a good illuminating efficiency can be obtained. Further, byarranging the slits at a specified angle, the brightness differencebetween the slits and portions other than the slits is made smallerwithin the observer's field of view, so that a successful image qualityof reflected light can be maintained.

[0182] According to the present invention, light emitted from the lightsource is collimated by the collimator and introduced to the firstsubstrate. The light incident on the first substrate is totallyreflected by the slopes of the first substrate, where the angle of lightis changed so as to be smaller than the total reflection angle, thusbeing outputted to the bottom face side.

[0183] Also, the light outputted from the bottom face of the firstsubstrate illuminates an illumination object, and reflected light fromthe illumination object is made to be incident again on the firstsubstrate, where the presence of the second substrate eliminates anydistortion of the image, and if

θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)},

[0184] a successful image can be displayed without being affected by theangle of visibility.

[0185] Also, if the light outgoing angle of the collimator is within±{90−θ− sin⁻¹(n₁/n)}, then all of the beams of light emitted from thelight source can be totally reflected by the slopes of the firstsubstrate to illuminate the illumination object therewith, thus offeringa good illuminating efficiency.

[0186] Thus, an illuminating system which makes the groove lines lessvisible, maintains image quality of reflected light successful andoffers a good illuminating efficiency can be provided.

[0187] In other words, according to the present invention, a lightsource, for example a linear light source, is placed beside a side faceof a light guide member as an example of a first transparent plate, andlight emitted from the light source is collimated by a collimator. Also,in the configuration of the light guide member, a bottom face of thelight guide member is a plane surface and slopes are provided at aspecified angle in the top face of the light guide member, and to thislight guide member is bonded a compensating plate as an example of asecond transparent plate whose top face is a plane surface and whosebottom face has grooves of the same configuration as in the light guidemember formed therein, by which most of the light that propagates withinthe light guide member is totally reflected by the stepwise slopes ofthe light guide member so as to be outputted from the light guidemember, thus allowing the reflecting plate as an example of theillumination object to be illuminated. Further, because the presence ofthe compensating plate allows the reflected light from the reflectingplate to be transmitted to the observer's side without being distorted,a successful image quality of the reflecting plate can be maintained.Further, because the light emitted from the light source is collimatedinto a specified angle by the collimator, the light is not transmittedfrom the light guide member to the compensating plate, allowing thereflecting plate to be illuminated with high efficiency and besidesmaking the groove lines less visible. Further, by making the stepwiseslopes into a specified angle, the brightness difference between thestepwise slopes and portions other than the slopes can be made smallerwithin the observer's field of view, so that a successful image qualityof the reflected light can be maintained.

[0188] Further, according to still another aspect of the presentinvention, the collimator which satisfies the output characteristicnecessary for the light guide member can be implemented, and the sameeffects as in the foregoing aspects can also be obtained.

[0189]FIG. 35 is a schematic cross-sectional view of an illuminatingsystem. As shown in FIG. 35, the illuminating system comprises a lightsource 101, a reflector 102, a light guide member 103 and a compensatingplate 105. In order that the reflector 102 collimates the light emittedfrom the light source 101, the distance from the light source 101 to aside face of the light guide member 103 is elongated. The light guidemember 103 has a function of totally reflecting and propagating thelight introduced from the reflector 102, and a function of illuminatinga reflecting plate 104 by totally reflecting the light with slopes ofgrooves formed in its top face to change the angle of the light. Thecompensating plate 105 has a function of correcting any distortion thatoccurs when the reflected light from the reflecting plate 104 passes thelight guide member 103.

[0190] However, since the illuminating system has a double sheetconstruction of the light guide member 103 and the compensating plate105 and since the light guide member 103 and the compensating plate 105are bonded together with their grooves identical in shape, theiralignment may be difficult to accomplish and the fabrication costs high.

[0191] Therefore, following embodiments of the present invention have anaim of solving these issues.

[0192] Hereinbelow, an illuminating system by overhead irradiationaccording to a third embodiment of the present invention is describedwith reference to the accompanying drawings.

[0193]FIGS. 19 and 32 are a schematic view and a more detailed schematicview, respectively, of a cross section of the illuminating system byoverhead irradiation in the third embodiment of the invention.

[0194] Referring to FIG. 1, reference numeral 1 denotes a light source,in which a plurality of, for example, fluorescent lamps, such as hotcathode-ray tubes or cold cathode-ray tubes, or light emitting diodesare arrayed in a linear shape, or in which incandescent lamps or organiclight-emitting materials are formed into a linear shape. The lightsource 1 is arranged on one side of a light guide member 203.

[0195] In FIG. 19, reference numeral 2 denotes a reflector, which isplaced so as to cover the light source 1, and of which the inner surfaceis so made as to have a high reflectance and a small diffusivity. Forexample, the reflector is made up by depositing a high-reflectancematerial such as silver or aluminum on a resin sheet, and bonding thissheet to a thin metal plate or resin sheet. When the light source 1 is afluorescent lamp, it is desirable to fill the gap between the lightsource 1 and the reflector 2 with a material having a refractive indexclose to the glass' refractive index of 1.5. It is also desirable thatthe thickness of one side face of the light guide member 203 on thelight source 1 side and the height of the reflector 2 are equal to eachother.

[0196] In FIG. 19, a light guide member 203 is, as an example, atransparent plate (hereinafter, referred to as light guide member),which is made from a material such as quartz, glass, transparent resinlike acrylic resin or polycarbonate, or the like. As shown in FIG. 20,the light guide member 203 is set to a size equivalent to the size of anillumination object. A bottom face 232 and an incident surface 233 ofthe light guide member 203 form an angle of about 90 degrees. The lightguide member 203 is generally wedge shaped as a whole, and a top face231 of the light guide member 203 is tilted so as to be gradually closerto the bottom face 232 of the light guide member 203 with increasingdistance from the light source 1. That is, if the thickness of the sideface 233 of the light guide member 203 on the light source side is d1and the thickness of the other side face on the side opposite to thelight source 1 is d2, then d1≧d2. The relationship of these thicknessesmay be that d1=d2 basically, but a relationship of d1>d2 allows thebrightness to be maintained uniform, further favorably. Also, aplurality of V-shaped grooves 204 are formed in the top face 231 of thelight guide member 203.

[0197]FIG. 21 shows a detailed view of the groove 204. The groove 204 isformed so as to extend generally parallel to the longitudinal directionof the light source 1 (a direction vertical to the drawing sheet), andV-shaped in its cross section. A slope of the groove 204 on the lightsource side is referred to as a first slope 241. A slope of the groove204 on the side opposite to the light source 1 is referred to as asecond slope 242. Further, a portion of the light guide member top face231 where no groove 204 is present is referred to as a flat portion 243.The flat portions 243 constitute a part of the top face 231 that are oneplane. An angle θ₁ formed by the light guide member bottom face 232 andthe first slope 241 of the groove 204 is within a range thatθ₁≦90°−θ_(c)+2θ₃ and that θ₁≈ 45°θ₃−(½)sin⁻¹(1/n×sinβ), where θ_(c) isthe total reflection angle, θ₃ is the angle formed by the flat portion243 and the light guide member bottom face 232 and β is the angle formedby a perpendicular of the bottom face 232 and the observers direction.In addition, in FIG. 21, reference numeral 332 denotes an imaginaryplane parallel to the bottom face 232.

[0198] An angle θ₂ formed by the light guide member bottom face 232 andthe second slope 242 of the groove 204 is that θ₂≦(½)sin⁻¹(1/n), where nis the refractive index of the light guide member 203.

[0199] It is noted that as shown in FIG. 20, both pitch p and depth h ofthe groove 204 are based on the top face 231 as a reference plane.

[0200] In FIG. 19, on the other hand, reference numeral 205 denotes areflecting surface. The reflecting surface 205 is a printed article suchas a book or photograph, a screen display unit of personal computers orother office automation equipment, portable information terminals,portable video tape recorders and the like, or a reflection type liquidcrystal display used in various monitors.

[0201] Also in FIG. 19, reference numeral 206 denotes an observer (moreprecisely, an observer's eye). The observer 206 views the reflectingsurface 205 through the light guide member 203.

[0202] Next, operation of the illuminating system according to the thirdembodiment of the present invention is described.

[0203] Light that has been thrown from the light source 1 to be incidenton the light guide member 203 at its incident surface 233 results inlight having a radiation distribution of ±sin⁻¹(1/n) centered on the 0°direction according to Snell's law, given that the refractive index ofthe light guide member 203 is n. Since most of the material of the lightguide member 203 has a refractive index of not less than 1.42, theradiation distribution falls within a range of ±44.77°. Therefore, theincident light beam propagates within the light guide member 203 at theradiation distribution of ±44.77°. The light beam incident on the lightguide member bottom face 232 has an incident angle of 90°−44.77°=45.23°or more, which is larger than the total reflection angle, so that thelight beam is totally reflected by the light guide member bottom face232.

[0204] Next, operation of the light at the light guide member top face231 is described with reference to the accompanying drawings. The lightguide member top face 231 is so structured that a plurality of the flatportion 243 and a plurality of the grooves 204 each composed of thefirst slope 241 and the second slope 242 are arranged, and thereflection at the light guide member top face 231 is classified into thefollowing five patterns as shown in FIGS. 22A-22E. The first pattern ofFIG. 22A is light incident on the flat portion 243. A second pattern ofFIG. 22B is light incident on the first slope 241. A third pattern ofFIG. 22C is light incident on the second slope 242. In the followingdescription, α is assumed to be an angle formed by the light guidemember bottom face 232 and the light reaching the light guide member topface 231. Because the light reaching the light guide member top face 231is light having a distribution of the positive direction out of thelight having the radiation distribution of ±sin⁻¹(1/n) centered on 0°, ais not less than 0° and the light has the maximum radiation distributionat 0°.

[0205] In the first pattern of FIG. 22A, the light is incident on theflat portion 243 at an incident angle of {90°−α−θ₃}. Because θ₃ is asmall value, most of light is reflected. The light reflected by the flatportion 243 results in an angle of {−α−2×θ₃}.

[0206] In the second pattern of FIG. 22B, the light is incident on thefirst slope 241 at an incident angle of {90°−α−θ₁}. The light that hasbeen incident on the first slope 241 is partly reflected by Fresnelreflection and partly transmitted to be a loss. The light reflected bythe first slope 241 results in an angle of light of {−α−2×θ₁}.

[0207] In the third pattern of FIG. 22C, the light is incident on thesecond slope 242 at an incident angle of {90°−α+θ₂}. Since the lightreflected by the second slope 242 results in an angle of light of{−α+2×θ₂}, the reflected light, when θ₂ is a small value, results inmore parallel light than the light which is prior to the reflection.

[0208] Actually, the light is reflected in a composite combination ofthe first to third patterns. Although not limited because of differencesdepending on the size of the illuminating system, the groove height h isset to around 5 μm-25 μm and the pitch p is set to around 100 μm to 250μm in this case. As a result, not a few rays of light, after beingreflected by the flat portion 243, are reflected by the first slope 241(in a combination of the first pattern and the second pattern). Thispattern is referred to as a fourth pattern of FIG. 22D.

[0209] In the fourth pattern of FIG. 22D, the light is incident on thefirst slope 241 at an incident angle of {90°−(−α−2×θ₃)−θ₁}. In thiscase, since θ₁ satisfies that θ₁≦90°−θ_(c)+2θ₃, the incident angle ontothe first slope 241 is 90°−(−α−2×θ₃)−θ₁≧α+θ_(c) (where θ_(c) is thetotal reflection angle). Because α is not less than 0°, all the rays oflight are larger than the total reflection angle and are totallyreflected, preferably. In addition, θ₁, when not more than 20°, wouldcause a difficulty in the view of the observer 206, so that θ₁ ispreferably set to an angle over 20°.

[0210] The light reflected by the first slope 241 results in an angle oflight of {α+2×θ₃−2×θ₁}, and becomes incident on the light guide memberbottom face 232 at an incident angle of {90°+α+2×θ₃−2×θ₁}. In this case,since θ₁ satisfies that θ₁≈45°+θ₃−(½)sin⁻¹(1/n×sinβ), the incident angleon the bottom face 232 is 90°+α+2×θ₃−2×9θ₁≈α+sin⁻¹(1/n×sinβ). It isnoted here that β is the angle formed by the direction perpendicular tothe reflecting surface 205 and the direction of observation by theobserver 206 as shown in FIG. 19, that is, β indicates the direction ofthe observer 206.

[0211] Since α is at most 0°, the light is incident on the bottom faceat an angle distribution centered on the angle sin⁻¹(1/n×sinβ).Accordingly, the light goes out from the light guide member bottom face232 at an angle distribution centered on the angle β, which is favorablefor observation in the direction of angle β, thus allowing an adjust toa direction easier for the observer to view. Also, the closer to 0° thevalue of α is, the narrower the radiation angle distribution centered onthe direction of angle β becomes, preferably.

[0212] Also, when θ₂ is a small value, not a few rays of light, afterbeing reflected by the second slope 242, are reflected by the flatportion 243 to be incident on the first slope 241 (a combination of thefirst, second, and third patterns). This pattern is referred to as afifth pattern of FIG. 22E.

[0213] In the fifth pattern of FIG. 22E, since the light reflected bythe second slope 242 results in {−α+2×θ₂}, the reflected light, when θ₂is a small value, results in more parallel light than before it isreflected. Therefore, the light reflected by the second slope 242 istotally reflected by the flat portion 243 and the first slope 241 asdescribed in the fourth pattern of FIG. 22D, and the distribution ofradiation angle from the light guide member bottom face 232 after thetotal reflection becomes narrower, preferably.

[0214] Although not limited because of differences depending on the sizeof the illuminating system, the concrete value of θ₂ is at least such anangle that light reaches the second slope 242 and results in parallelrays of light. Therefore, θ₂ is such an angle that a ray of light havingthe maximum angle of α, sin⁻¹(1/n) is reflected toward the 0° direction,i.e., θ₂≦(½)sin⁻¹(1/n).

[0215] Further, on the assumption that the flat portion 243 is absent,the necessity of the flat portion 243 is described below. Out of thelight that reaches the light guide member top face 231, light of 0<α<θ₂cannot reach the second slope 242, as can be easily understood, thusreaching the first slope 241. Therefore, the light is partly reflectedby Fresnel reflection but partly transmitted to be a loss. Also, lightof θ₂<α<2θ₂, when reflected by the second slope 242, results in a ray oflight having an angle of −α+2θ₂ as described in the third pattern, sothat 0<αθ₂. Accordingly, the light is Fresnel-reflected by the firstslope 241 or transmitted to be a loss. Further, light of2θ₂<α<{sin⁻¹(1/n)} is reflected by the second slope 242 so that{−sin⁻¹(1/n)+2θ₂}<α<0. The light that is reflected by the second slope242 partly reaches the first slope 241 successfully, but partly does notreach the first slope 241 so as to be directed toward the light guidemember bottom face 232. Therefore, the rate of light of 0<α<θ₂ increasesso that the light is transmitted by the first slope 241 to be a loss ata higher probability. Hence it can be said that the flat portion 243 isnecessary.

[0216] As a result of the above, light reflected by the grooves 204 isoutputted from the bottom face 232 of the light guide member 203. Itsoutgoing angle, although not limited because of differences depending onthe characteristics of the reflecting plate 205, is desirably along thedirection β in which the observer 206 usually observes.

[0217] Light outputted from the light guide member bottom face 232reaches the reflecting plate 205, being thereby reflected. The reflectedlight passes again through the light guide member 203, reaching theobserver 206. When this occur, a large distortion of the light guidemember 203 due to the grooves 204 would cause groove lines to beconspicuous, inappropriately.

[0218] However, if the grooves 204 are provided at such a pitch p notmore than the minimum resolution (dot pitch) of the reflecting plate 205that moire fringes are not formed, only the light transmittance of eachdot affects the image quality and the distortion of each dot does neveraffects the image quality.

[0219] Further, although not limited because of differences amongapplications, a length x of the first slope 241 of the groove 204, ifnot more than {L×(0.5/60)×_(π)/180}, makes the groove linesinconspicuous on the ground that the human eye's minimum resolution is0.5 minute, where L is the distance at which usually the screen isviewed (a distance between the observer 206 and the top face 231 of thelight guide member 203). For example, if L is 35 cm, then groove linesof not more than {35×(0.5/60)×π/180}=50 μm can be said to beinconspicuous.

[0220] Thus, it is preferable that the pitch p is not more than the dotpitch of the reflecting plate 205 or that the length x=h/tan(θ₁) of thefirst slope 241 is not more than (L×(0.5/60)×π/180}, where L is thedistance at which the observer 206 usually views the screen (thedistance between the observer 206 and the top face 231 of the lightguide member 203), in which case the groove lines are inconspicuous.

[0221] As shown above, the light emitted from the light source 1 isoutputted from the light guide member bottom face 232 by the firstslopes 241 of the grooves 204, illuminating the reflecting plate 205, inwhich case the light density would decrease with increasing distancefrom the light source 1, resulting in non-uniform brightnessdistribution. However, because the thickness d1 of the side face of thelight guide member 203 on the light source 1 side and the thickness d2of the side face of the light guide member 203 on the side opposite tothe light source 1 have a relationship of d1≧d2, the light density ismaintained constant so that the brightness distribution becomesconstant.

[0222] It is also preferable to make the pitch p decreasing withincreasing distance from the light source 1, in which case thebrightness distribution becomes more uniform.

[0223] It is also preferable to increase the depth h at places far fromthe light source 1, in which case the brightness distribution becomesmore uniform.

[0224] Thus, according to this third embodiment, there can be providedthe illuminating system by overhead irradiation which is simple inconstruction, good at illuminating efficiency, inconspicuous in groovelines and uniform in brightness distribution.

[0225] Concrete numerical values for the third embodiment may beexemplified as follows. From the viewpoint of a setting under thecritical angle, a value of θ₁<49.8° is set in the condition thatθ₁≦90°−θ_(c)+2θ₃, for an improvement of brightness. Also, the outgoingangle is set by setting a value of θ₁≈46.2° for β=30° in the conditionthat θ₁≈45°+θ₃−(½)sin⁻¹(1/n×sinβ). Also, from the viewpoint of improvingthe reflectance at the first slope 241 of the groove 204 of the lightguide member 203 by making the rays of light parallel, a value ofθ₂≦20.9° is set in the condition that θ₂≦(½)sin⁻¹(1/n), for animprovement of brightness. Further, the pitch p of the grooves 204 isset to not more than 250 μm so as to be not more than the dot pitch ofthe reflecting plate 205, for a reduction in the groove lines. Further,a value of x≦50.9 μm is set in the condition that the length of thefirst slope 241 of the groove 204, x≦{L×(0.5/60)×π/180}, for a reductionof the groove lines. In addition, this example is based on theassumption that the refractive index of the light guide member 203,n=1.5, the angle formed by the top face 231 and the bottom face 232 ofthe light guide member 203, θ₃=0.8° and that the distance between thetop face 231 of the light guide member 203 and the observer 206, L=350mm.

[0226] In the third embodiment, it was found as a result of simulationexperiments that the length of the flat portion is preferably about fivetimes as long as the length of the first slope, in which case rays oflight in the fifth pattern account for larger portion.

[0227] It is noted here that the present invention is not limited to theabove third embodiment, and may be embodied in various ways.

[0228] For example, it is preferable to provide a protective layer onthe surface of the light guide member 203 in the third embodiment, inwhich case deteriorations of the appearance due to flaws or the like canbe prevented. Hard coating agents as an example of the material thatforms the protective layer can be exemplified by thermosetting siliconbase agents with importance laid on the coating function,ultraviolet-curing acrylic agents or ultraviolet-curing silicon baseagents with importance laid on the coating workability, and the like.

[0229] Further, in the third embodiment, a transparent sheet made ofacryl or polycarbonate or the like may be provided instead of theprotective layer. It is also possible to provide a protective layer onthese transparent sheets.

[0230] It is also preferable to provide an antireflection coating on thetop face 231 of the light guide member 203 in the third embodiment, inwhich case the image from the reflecting plate 205 becomes sharp.

[0231] It is also possible that a collimator for collimating the lightof the horizontal direction with respect to the light source 1 isattached to a side face 233 of the light guide member 203 on the lightsource side in the third embodiment. The radiation distribution of lightemitted from the light source 1 has a spread in not only the verticaldirection but also horizontal direction to the light source 1. On thisaccount, the light can be effectively utilized by suppressing thehorizontal rays of light by the collimator. In other words, the frontbrightness is enhanced by narrowing the radiation brightnessdistribution in both right and left directions.

[0232] Furthermore, as a modification of the third embodiment, two ormore fluorescent lamps may be used for a large-screen reflecting platewith a 13 inch or more diagonal, by which the brightness can bemaintained, favorably. Examples of this modification are shown in FIGS.23A, 23B, 23C. One exemplary way is, as shown in FIG. 23A, to place twoor more lamps at the site of the light source 1. Another way is, asshown in FIG. 23B, to prepare two light guide members 203 of the thirdembodiment and placed them opposite to each other with theirsmaller-thickness side faces adjoining. With this constitution, lightemitted from a right-side light source 211 is internally reflected by atop face 311 of the right-side light guide member 203 so as to beoutputted from a bottom face 321, while light emitted from a left-sidelight source 212 is internally reflected by a top face 312 of theleft-side light guide member 203 so as to be outputted from a bottomface 322, so that the brightness is maintained for the large screen,favorably.

[0233] Still another way is, as shown in FIG. 23C, to prepare two lightguide members 203 of the third embodiment and position them back to backwith their larger-thickness side faces adjoining. With thisconstitution, light emitted from a right-side light source 211 isinternally reflected by a top face 312 of the left-side light guidemember 203 so as to be outputted from a bottom face 322, while lightemitted from a left-side light source 212 is internally reflected by atop face 311 of the right-side light guide member 203 so as to beoutputted from a bottom face 321, so that the brightness is maintainedfor the large screen, favorably.

[0234] For a small-screen reflecting plate with a 4 inch or lessdiagonal, employing light emitting diodes or the like as the lightsource 1 is suited for miniaturization, preferably. In this case,because the radiation distribution of light emitting diodes has somedegree of directivity, the reflector 2 may be omitted.

[0235] As described above, according to the third embodiment, lightemitted from the light source 1 becomes incident on the light guidemember 203, and propagates on and on while being iteratively totallyreflected within the light guide member 203. During this process, thelight is totally reflected by the grooves 204, . . . , 204 provided inthe top face of the light guide member 203, being changed into an angleof light smaller than the total reflection angle and so outputted to thebottom face side, thus illuminating an illumination object 205. Thereflection at the grooves 204 is composite reflection at the firstslopes 241, the second slopes 242 and the flat portions 243. Therefore,if the angle of the first slope 241 is not more than {90°−θ_(c)+2θ₃},the reflectance becomes high so that the illuminating efficiency isimproved.

[0236] Further, the angle of light emitted from the light guide member203 by the first slope 241 varies. On this account, if the angle of thefirst slope 241 is {45°+θ₃−(½)sin⁻¹(1/n×sinβ)}, then the angle ofoutgoing light becomes in the β direction so that angle of outgoinglight can be aligned along the easy-to-view angle for the observer 206.

[0237] Also, if the angle of the second slope 242 is not more than{(½)sin⁻¹(1/n)}, then the light reflected by the second slope 242becomes more parallel rays of light. On this account, the light thatreaches the first slope 241 or the flat portion 243 after beingreflected by the second slope 242 is reflected at higher reflectance.Thus, the illuminating efficiency is improved.

[0238] Further, if the pitch of the grooves 204, . . . , 204 is not morethan the dot pitch of the illumination object 205, then the groove linesbecome inconspicuous so as not to be an obstacle to the observer 206.

[0239] Also, if the length x of the first slope 241 is not more than{L×(0.5/60)×π/180}, where L is the distance between the observer 206 andthe top face of the light guide member 203, then the groove lines becomeinconspicuous so as not to be an obstacle to the observer 206 on theground that the human eye's resolution is 0.5 minute.

[0240] Thus, there can be provided the illuminating system by overheadirradiation which is simple in construction, good at illuminatingefficiency and inconspicuous in groove lines.

[0241] Next, an illuminating system by overhead irradiation according toa fourth embodiment of the present invention is described with referenceto the accompanying drawings.

[0242] The illuminating system of the fourth embodiment of the inventionis generally similar in construction to the illuminating system of thethird embodiment, and differs therefrom only in that a transparent plate207 is placed on the light guide member 203.

[0243] In FIGS. 24 and 33, reference numeral 207 denotes a transparentplate (hereinafter, referred to as prism sheet), which is made from amaterial such as quartz, glass, transparent resin like acrylic resin orpolycarbonate, or the like. In particular, a transparent resin, whenused, may be a soft material formed into a sheet shape.

[0244] One side of the prism sheet 207 is a flat surface 271, and theother side is a prism surface 272 with the cross section formed into atriangular, wedge shape. The shape of the prism sheet 207 is generallyequal in size to the light guide member 203, as viewed from the top. Onthe prism surface 272 of the prism sheet 207, are arrayed a plurality ofcombinations of at least an isosceles-triangular (or equilateraltriangular, possible) wedge-shaped projected portion 273 (hereinafter,referred to as prism portion) and a flat portion 274 as shown in FIG.25, where the wedge-shaped projected portions 273 with anisosceles-triangular cross section each extend parallel to thelongitudinal direction of the light source 1 and are arranged at theintervals of the pitch P in a direction perpendicular to thelongitudinal direction. If the angle formed by each slope of theprojected portions 273 with an isosceles-triangular cross section and animaginary plane parallel to the flat surface 271 is θ₄, then θ₄ ispreferably set within a range of 30° to 50° in order that the prismsheet 207 effectively works. The prism sheet 207 is placed on the topface of the light guide member 203 with the prism surface 272 downside.

[0245] Next, operation of the illuminating system in the fourthembodiment is described.

[0246] Some of the light that has been incident on the light guidemember 203 from the light source 1 is transmitted through the firstslopes 241 of the grooves 204. This ray of light has a large outgoingangle with respect to the top face 231 of the light guide member 203.For example, the light is outputted in a direction in the vicinity of80° in the foregoing third embodiment. FIG. 26 shows a graph ofcharacteristics of light outputted from the light guide member top face231 under the conditions of θ₁=40° and θ2 ₌₁₀°. In FIG. 26, it can beunderstood that the leakage amount of light becomes large at outgoingangles around 70°-80°. Accordingly, the light, upon reaching the prismsurface 272 of the prism sheet 207, is reflected by the triangularprojected portions 273 as illustrated in FIG. 27 so as to be incidentagain on the light guide member 203 and pass through the light guidemember 203, thus reaching the reflecting plate 205. In this process, itwas derived from experiments and simulations that slope angles θ₄ withina range of 30° to 50° allow a good efficiency to be obtained. As aresult of this, the light illuminating efficiency is improved so thatthe brightness is enhanced.

[0247] Also, the light (image) reflected by the reflecting plate 205would yield distortion when passing through the light guide member 203and the prism sheet 207. However, the cross section of the prism sheet207 having the flat portions 274, given a large length ratio of the flatportion 274 to the slope of the prism portions 273 and a small pitch Pof the prism portions 273, then less distortion results. That is, whenthe prism portions 273 are provided at a pitch not more than the minimumresolution (dot pitch) of the reflecting plate, only the lighttransmittance of each dot affects the image quality and the distortionof each dot never affects the image quality.

[0248] Further, although not limited because of differences amongapplications, a length x of the slope, if not more than{L×(0.5/60)×_(π)/180}, makes the prism-portion lines inconspicuous onthe ground that the human eye's minimum resolution is 0.5 minute, whereL is the distance at which usually the screen is viewed. For example, ifL is 35 cm, then prism-portion lines of not more than 50 μm can be saidto be inconspicuous.

[0249] Thus, it is preferable that the pitch p of the prism portions 273is not more than the dot pitch of the reflecting plate or that thelength of the slope of the prism portions 273 is not more than{L×(0.5/60)×_(π)/180}, where L is the distance at which the observerusually views the screen (the distance between the observer and the topface of the prism sheet), in which case the lines of the projectedportions 273 are inconspicuous.

[0250] As concrete examples of numerical values, the angle θ₄ of theslope is set to within a range of 30° to 50° for recycling of leakagelight, while the pitch p is set to not more than 250 μm so as to be notmore than the dot pitch of the reflecting plate 205, for reduction inthe prism-portion lines. Further, the length of the slope of the prismportions is set to not more than 50.9 μm so as to be not more than{L×(0.5/60)×_(π)/180}, for reduction of the prism-portion lines.

[0251] The prism sheet 207, which is intended to recycle the light thathas leaked from the light guide member 203 by reflecting it at theslopes, may be implemented in other shapes only if slopes and a flatportion similar to those of the above embodiment are provided. FIGS. 28Aand 28B show examples of other shapes. For example, the prism sheet 207can be implemented by one arrangement in which a plurality of grooves276 each having a triangular cross section are arranged as shown in FIG.28A, or another in which a plurality of hills 277 each having atrapezoidal cross section are arranged as shown in FIG. 28B, or the like(see FIG. 33).

[0252] Further, the radiation distribution of light emitted from thelight source 1 has a spread in not only the vertical direction but alsohorizontal direction to the light source. Therefore, by placing theprism sheet 207 in such a direction of the prism that the projectedportions or the like extend in a direction perpendicular to thelongitudinal direction of the light source 1, component rays of light inthe direction horizontal to the light source 1 are reflected by theslopes so as to pass again through the light guide member 203 andilluminate the reflecting plate 205, by which the illuminatingefficiency can be improved.

[0253] Therefore, according to the fourth embodiment, light emitted fromthe light source 1 becomes incident on the light guide member 203, andpropagates on and on while being iteratively totally reflected withinthe light guide member 203. During this process, the light is totallyreflected by the grooves 204, . . . , 204 provided in the top face 231of the light guide member 203, being changed into an angle of lightsmaller than the total reflection angle and so outputted to the bottomface side, thus illuminating the illumination object 205. The reflectionat the grooves 204 is composite reflection at the first slope 241, thesecond slope 242 and the flat portion 243. Therefore, part of the lightis outputted from the top face 231 of the light guide member 203 by thefirst slopes 241. The light outputted from the light guide member topface 231 is reflected by the slopes of the bottom face of the prismsheet 207 so as to be incident again on the light guide member 203, thusilluminating the illumination object 205. Thus, the illuminatingefficiency is improved.

[0254] Also, since the angle θ₄ of the slopes of the prism sheet 207 iswithin the range of 30° to 50°, a more efficient illumination can beachieved.

[0255] Also, if the pitch P of the slopes of the prism sheet 207 is notmore than the dot pitch of the illumination object 205, the lines of theprism sheet 207 become inconspicuous so as not to be an obstacle to theobserver 206.

[0256] Further, if the length of the slope is not more than{L×(0.5/60)×_(π)/180}, where L is the distance between the observer 206and the top face 271 of the prism sheet 207, then the prism-portionlines become inconspicuous so as not to be an obstacle to the observer206 on the ground that the human eye's resolution is 0.5 minute. Thus,there can be provided the illuminating system by overhead irradiationwhich is simple in construction, good at illuminating efficiency andinconspicuous in prism-portion lines.

[0257] Next, an illuminating system by overhead irradiation according toa fifth embodiment of the present invention is described.

[0258] The illuminating system of the fifth embodiment of the inventionis generally similar in construction to the illuminating system of thefourth embodiment, and differs therefrom only in the way how the prismsheet is positioned. The prism sheet 207 in this embodiment ispositioned with the prism surface 272 upside.

[0259] The operation in this case is described with reference to FIGS.29 and 34. Reflected light, although varying depending on thecharacteristics of the reflecting plate 205, is generally diffusedlight. On this account, the light is radiated also in directions out ofthe angle of visibility. This light out of the angle of visibility iscondensed by the prism surface 272 of the prism sheet 207, by which thefront brightness is improved.

[0260] Assume that the reflected light is distributed around a center ofa direction generally vertical to the light guide member 203 and theprism sheet 207 (the center direction is here assumed to be 0°). Thereflected light passes through the light guide member 203 so as to beincident on a flat portion 274 of the prism sheet 207. Assuming that thereflecting plate 205 is a complete diffusing plate, the light afterbeing incident on the prism sheet 207 is distributed to ±sin⁻¹(1/n₁)around the 0° direction, where n₁ is the refractive index of the prismsheet 207.

[0261] As shown in FIG. 29, if the angle formed by the flat surface 271and the slope of the prism portions 273 of the prism sheet 207 is θ₄,then the outgoing angle is {θ₄+sin⁻¹(n×sin(α−θ₄))}. Given a θ₄ of 50°and n₁=1.5, the maximum value of α₁+sin⁻¹(1/n₁), is 41.8°, the outgoingangle being 37.7°, which is smaller than ±90°, an angle before theincidence on the prism sheet. On this account, the radiationdistribution of the reflected light is narrowed by the slopes of theprism sheet 207. It was derived from experiments and simulations thatslope angles θ₄ within a range of 30° to 50° allow a good efficiency tobe obtained. That is, with the slope angle in this range, the radiationangle distribute of reflected light can be narrowed so that the frontbrightness is enhanced.

[0262] As shown above, by positioning the prism surface 272 upside, thefront brightness can be improved.

[0263] Also, the reflecting plate 205 may be other than a completediffusing surface or other the outgoing angle of the light guide member203 may be other than 0°, in which case also the radiation distributioncan be narrowed in a similar manner, preferably.

[0264] Also, the light (image) reflected by the reflecting plate 204would yield distortion when passing through the light guide member 203and the prism sheet 207. However, the cross section of the prism sheet207 having the flat portions 274, given a large length ratio of the flatportion 274 to the slope portion of the prism portions 273 and a smallpitch of the prism portions 273, then less distortion results. That is,when the grooves are provided at a pitch not more than the minimumresolution (dot pitch) of the reflecting plate, only the lighttransmittance of each dot affects the image quality and the distortionof each dot never affects the image quality.

[0265] Further, although not limited because of differences amongapplications, a length x of the slope, if not more than(L×(0.5/60)×_(π)/180}, makes the prism-portion lines inconspicuous onthe ground that the human eye's minimum resolution is 0.5 minute, whereL is the distance at which usually the screen is viewed. For example, ifL is 35 cm, then prism-portion lines of not more than 50 μm can be saidto be inconspicuous.

[0266] Thus, it is preferable that the pitch P is not more than the dotpitch of the reflecting plate or that the length of the slope is notmore than (L×(0.5/60)×_(π)/180}, where L is the distance at which theobserver usually views the screen, in which case the prism-portion linesare inconspicuous.

[0267] Examples of concrete numerical values are the same as in thefourth embodiment.

[0268] In this fifth embodiment, the prism sheet 207, which is intendedto improve the front brightness by condensing the light out of the angleof visibility by the prism surface 272 of the prism sheet 207, may beimplemented in other shapes only if slopes and flat portions similar tothose of the fifth embodiment are provided. FIG. 34 shows an example ofother shapes. For example, out of the three kinds of prism sheets 207 inFIG. 34, a prism sheet on the left side is the prism sheet 207 of FIG.29, while a prism sheet on the upper right side is one in which aplurality of grooves 276 each having a triangular cross section arearranged in its top face. A prism sheet on the lower right side is onein which a plurality of hills 277 each having a trapezoidal crosssection are arranged in its top face. With these prism sheets, similarfunctions can be accomplished.

[0269] Also, as can be easily understood from the above description, thelongitudinal direction of the prism of the prism sheet 207 is notlimited.

[0270] Therefore, according to the fifth embodiment, by arranging on thelight guide member 203 a prism sheet 207 comprising a transparent platein which, with respect to a cross-sectional shape, a plurality ofprojected portions 273 having slopes of an angle θ₄ to the bottom faceare arranged on the top face so that a flat portion (274) generallyparallel to the top face is interposed therebetween. Thus, the radiationdistribution of reflected light from the illumination object 205 can benarrowed so that the front brightness can be improved.

[0271] Also, if the pitch p of the slope of the prism sheet 207 is notmore than the dot pitch of the illumination object 205, the lines of theprism sheet 207 are inconspicuous so as not to be an obstacle to theobserver 206.

[0272] Also, if the length of the slope is not more than{L×(0.5/60)×_(π)/180}, where L is the distance between the observer 206and the top face of the prism sheet 207, the groove lines becomeinconspicuous so as not to be an obstacle to the observer 206 on theground that the human eye's resolution is 0.5 minute. Thus, there can beprovided the illuminating system by overhead irradiation which is simplein construction, good at illuminating efficiency and inconspicuous ingroove lines.

[0273] Next, an illuminating system by overhead irradiation according toa sixth embodiment of the present invention is described with referenceto the accompanying drawings. The illuminating system of the sixthembodiment of the invention is generally similar in construction to theilluminating system of the third embodiment, and differs therefrom onlyin the shape of the grooves of the light guide member 203.

[0274]FIG. 30 shows a view as viewed from above the illuminating system.Lateral grooves 204 are provided along a direction parallel to the lightsource 1. Besides, longitudinal grooves 208 are provided along adirection perpendicular to the light source 1. The lateral grooves 204are the same as the grooves 204 of the third embodiment. FIG. 31 shows across-sectional view of the longitudinal grooves 208. The longitudinalgrooves 208 are V-shaped grooves and an apex angle θ₅ of each groove 208is between 80° to 120°.

[0275] The radiation distribution of light emitted from the light source1 has a spread in not only the vertical direction but also horizontaldirection to the light source 1. Therefore, by placing the longitudinalgrooves 208, component rays of light in the direction horizontal to thelight source 1 are reflected by the slopes so as to go out from thelight guide member 203 and illuminate the reflecting plate 205, by whichthe illuminating efficiency can be improved. The present inventors maderepeated experiments and simulations, finding out that angles θ₅ withina range of 80° to 120° are effective. That is, with the angle θ₅ in thisrange, the brightness can be improved by effectively utilizing the lightin the direction parallel to the light source 1.

[0276] Examples of concrete numerical values for the pitch and the slopelength are the same as in the fourth embodiment.

[0277] Therefore, according to the sixth embodiment, light emitted fromthe light source 1 becomes incident on the light guide member 203, andpropagates on and on while being iteratively totally reflected withinthe light guide member 203. During this process, the light is totallyreflected by the grooves 204, . . . , 204 provided in the top face 231of the light guide member 203, being changed into an angle of lightsmaller than the total reflection angle and so outputted to the bottomface side, thus illuminating the illumination object 205.

[0278] The radiation distribution of light emitted from the light source1 has a spread in not only the vertical direction but also horizontaldirection to the light source 1. Therefore, by placing the longitudinalgrooves 208, . . . , 208, component rays of light in the directionhorizontal to the light source 1 are reflected by the slopes so as to goout from the light guide member 203 and illuminate the reflectingsurface, by which the illuminating efficiency can be improved.

[0279] Also, since each longitudinal groove 208 is formed into a V-shapeand the apex angle θ₅ of each longitudinal groove 208 falls within therange of 80° to 120°, a highly efficient illumination can be achieved.

[0280] Thus, there can be provided the illuminating system by overheadirradiation which is simple in construction, good at illuminatingefficiency and inconspicuous in groove lines.

[0281] As described above, according to one aspect of the presentinvention, the illuminating system by overhead irradiation at leastcomprises a light source, a transparent plate-shaped light guide member,at the side face of which the light source is located, in which aplurality of grooves are arranged in a top face of the light guidemember at specified intervals in a direction parallel to a longitudinaldirection of the light source, and in which flat portions constituting apart of the top face are arranged between adjacent ones of the grooves,wherein an illumination object placed on a bottom face side of the lightguide member is observed from a top face side of the light guide member.Therefore, most of light propagating within the light guide member canbe totally reflected by the grooves so as to go out from the light guidemember, thereby illuminating the reflecting surface.

[0282] Also, by setting the angle of the first slope of the grooves sothat θ₁≦90−θ_(c)+2θ₃, a more efficient illumination can be achieved.Also, by setting the angle θ₁ of the first slope so thatθ₁≈45°+θ₃−(½)sin⁻¹(1/n×sinβ), the outgoing angle can be aligned alongthe observer's direction β, favorably.

[0283] Also, setting the angle of the second slope of the grooves sothat θ₂≦(½)sin⁻¹(1/n), a more efficient illumination can be achieved.

[0284] Also, setting the pitch of the grooves to not more than the dotpitch of the illumination object, the groove lines can be madeinconspicuous.

[0285] Also, setting the length of the first slope to not more than{L×(0.5/60)×_(π)/180}, where L is the distance between the observer andthe illuminating system, more specifically, the top face of the lightguide member, the groove lines can be more inconspicuous.

[0286] According to the illuminating system by overhead irradiation inanother aspect of the present invention, a transparent prism sheet isplaced on the light guide member, the prism sheet having, with respectto a cross-sectional shape, a plurality of projected portions havingslopes of an angle θ₄ to the top face which are arranged on the bottomface so that a flat portion generally parallel to the bottom face isinterposed therebetween. Therefore, the light that has leaked from thelight guide member can be reflected by the slopes of the angle θ₄ so asto pass through the light guide member, thereby illuminating thereflecting plate.

[0287] Also, by setting the slope angle θ₄ to within a range of 30° to50°, the illuminating efficiency is more improved.

[0288] Also, by setting the pitch of the slope of the prism sheet to notmore than the dot pitch of the illumination object, the groove lines canbe made inconspicuous.

[0289] Also, by setting the length of the slope of the prism sheet tonot more than {L×(0.5/60)×_(π)/180}, where L is the distance between theobserver and the illuminating system, the groove lines can be moreinconspicuous.

[0290] According to the illuminating system by overhead irradiation instill another aspect of the present invention, a transparent prism sheetis placed on the light guide member, the prism sheet having, withrespect to a cross-sectional shape, a plurality of projected portionshaving slopes of an angle θ₄ to the bottom face which are arranged onthe top face so that a flat portion generally parallel to the top faceis interposed therebetween. Thus, the radiation distribution ofreflected light from the reflecting surface can be narrowed, by whichthe front brightness can be improved.

[0291] Also, by setting the pitch of the slopes of the prism sheet tonot more than the dot pitch of the illumination object, the groove linescan be made inconspicuous.

[0292] Also, by setting the length of the slope to not more than{L×(0.5/60)×_(π)/180}, where L is the distance between the observer andthe illuminating system, more specifically, the top face of the prismsheet, the groove lines can be made more inconspicuous.

[0293] Further, according to the illuminating system by overheadirradiation in yet another aspect of the present invention, a pluralityof grooves are arranged in the top face of the light guide member atspecified intervals in a direction perpendicular to a longitudinaldirection of the light source. Therefore, component rays of light in thedirection horizontal to the light source can be reflected by the slopesso as to go out from the light guide member and illuminate thereflecting surface. Thus, the illuminating efficiency can be improved.

[0294] Also, by setting the perpendicularly provided grooves into aV-shape, and by setting the apex angle θ₅ of the V-shape to within arange of 80° to 120°, the illuminating efficiency can be furtherimproved.

[0295] Further, with the liquid crystal display using any one of theilluminating systems as described above, a liquid crystal display whichcan succeed the advantages of the above illuminating systems can beachieved.

[0296] An illuminating system according to a seventh embodiment of thepresent invention will be described with reference to FIGS. 36, 37.

[0297]FIG. 36 is a diagram in cross section of the illuminating systemusing an example of a light guide member in the seventh embodiment ofthe present invention.

[0298] In FIG. 36, reference numeral 1 denotes a light source which is,for example, a fluorescent lamp such as a hot cathode ray tube or coldcathode ray tube, or an array of a plurality of light emitting diodes,or an incandescent lamp or a linearly shaped organic light-emittingmaterial, etc. The light source 1 is arranged at a side face of a lightguide member 303 of a transparent plate.

[0299] Reference numeral 2 denotes a reflector in FIG. 36 which isarranged to cover the light source 1. The reflector 2 is constituted sothat an inner face shows high reflectance and small diffusionperformance. For instance, silver, aluminum or the like material of highreflectance is vapor-deposited to a resin sheet, which is then bonded toa thin metallic plate or resin sheet, thereby to constitute thereflector. If the light source 1 is a fluorescent lamp, a gap betweenthe light source 1 and reflector 2 is preferably filled with a materialhaving a refractive index close to that of glass, namely, 1.5.

[0300] Preferably, a thickness of the side face of the light guidemember 303 at the side of the light source 1 is equal to a height of thereflector 2. When the light source 1 is composed of light emittingdiodes, the reflector 2 can be eliminated because a radial distributionof the light source has some level of directivity. In that case, thelight guide member 303 is desirably compact in size.

[0301] Still referring to FIG. 36, the light guide member 303 is, e.g.,a transparent plate (referred to simply as a “light guide member”hereinbelow) formed of quartz, glass, or transparent resin such asacrylic resin, polycarbonate, etc. The light guide member 303 is made inthe same size as that of an illumination object. As shown in FIG. 37, alower face 332 of the light guide member 303 is set to be approximately90° to a plane of incidence 343. The light guide member 303 isschematically shaped like a wedge as a whole, having an upper face 331tilted so as to be gradually closer to the lower face 332 withincreasing distance from the light source 1. More specifically,supposing that the thickness of the side face 333 of the light guidemember 303 at the side of the light source is d1, and a thickness of aside face of the light guide member at the side opposite to the lightsource 1 is d2, d1≧d2 is held. Although d1=d2 is fundamentallysatisfactory, a relation of the thicknesses of d1>d2 is more preferableto maintain a luminance constant. A plurality of V-shaped grooves 304are notched in the upper face 331 of the light guide member 303.

[0302] In FIG. 36, reference numeral 305 denotes a reflecting face whichis, for example, a printed article such as a book, a photograph or thelike, an image display device of a personal computer or other OfficeAutomation equipment, a portable information terminal, a portable videotape recorders, etc., or a reflecting-type liquid crystal display deviceused in various kinds of monitors.

[0303] The propagation of light in the illuminating system of theseventh embodiment will now be described.

[0304] Light projected from the light source 1 enters the light guidemember 303 directly or after being reflected at the reflector 2. Thelight entering the light guide member 303 is totally reflected andpropagates. The light reflected at the grooves 304 among the propagationlight loses total reflection conditions and consequently comes out fromthe lower face 332 of the light guide member.

[0305] At this time, the light is reflected at the lower face 332 of thelight guide member to be a reflected light 320. The light projected fromthe lower face 332 of the light guide member illuminates the reflectingface 305, when the light is reflected at the reflecting face 305 andbecomes a reflected light 500. The reflected light 500 is an imagegenerated by the reflecting face 305. The reflected light 320 is anunnecessary light worsening visibility of the image.

[0306] Meanwhile, in the seventh embodiment, the lower face 332 of thelight guide member is subjected to an anti-reflection treatment or adiffuse treatment by the known vacuum vapor deposition method, dipmethod, thermal transfer method, etc. When the lower face 32 isprocessed through the antireflection treatment, the total quantity ofthe reflected light from the lower face 332 designated by 320 in FIG. 36is reduced so large as is negligible enough in comparison with thequantity of the reflected light 500 from the reflecting face 305.Therefore, visibility can be improved greatly.

[0307] When the lower face 32 is processed through the diffusetreatment, the reflected light 320 from the lower face 332 of the lightguide member becomes irregularly reflected, whereby the quantity oflight sensed as bright lines by human eyes due to the mirror reflectionis reduced although the total quantity of the reflected light isunchanged, and the visibility can be improved.

[0308] However, the diffuse treatment to the lower face 332 causes thereflected light 500 from the reflecting face 305 to diffuse similarly,rather inviting blurring in outline of displayed characters, etc. anddecreasing the visibility. For avoiding this inconvenience, a haze valueof the diffuse treatment to the lower face 332 is preferably not largerthan 20%, particularly in a range of 4-10% to reduce bright lines of thereflected light 320 in a well-proportioned relation to the outlineblurring, as is detected from experiments with many people includingwomen and aged people. The “haze value” referred to here is a numericalvalue indicating a degree of diffusion, i.e., a ratio expressed by % ofa diffuse transmission light and a total transmission light.

[0309] Needless to say, the visibility can be naturally improvedfurthermore if both the anti-reflection treatment and the diffusetreatment are performed to the lower face 332 of the light guide member.

[0310] When an anti-reflection film is formed on the upper face 331 ofthe light guide member 303, the reflection by an external light can bealso reduced, with the visibility improved more.

[0311] A reflection type liquid crystal display device using the lightguide member according to the seventh embodiment of the presentinvention will be described with reference to FIG. 3.

[0312] Those parts of FIG. 38 denoted by the same numerals as in FIG. 36represent the same parts. 360 is a reflection type liquid crystal panelcomprised of two substrates 361 and 362. The lower face 332 of the lightguide member 303 is subjected to the anti-reflection treatment ordiffuse treatment in the known method, for example, vacuum vapordeposition, dipping, or thermal transfer method or the like. A surfaceof the substrate 361 of the reflection type liquid crystal panel 360 isalso processed through the anti-reflection treatment or diffusetreatment.

[0313] Because of the anti-reflection treatment to the lower face 332 ofthe light guide member or the surface of the substrate 361, the totalquantity of the reflected light 320 from the lower face 332 of the lightguide member or the reflected light 610 from the surface of thesubstrate 61 is reduced to a negligible level as compared with thequantity of a reflected light 600 from the liquid crystal panel 360. Thevisibility can consequently be enhanced.

[0314] It goes without saying that the anti-reflection treatment may beexecuted to both of the lower face 332 of the light guide member and thesurface of the substrate 361.

[0315] When the diffuse treatment is carried out to either the lowerface 332 of the light guide member or the surface of the substrate 361,the reflected light 320 from the lower face 332 or the reflected light610 from the surface of the substrate 361 is irregularly reflected. As aresult, the amount of light detected as bright lines by human eyes dueto the mirror reflection is reduced although the total amount of thereflected light is not changed, and accordingly the visibility can beimproved.

[0316] In spite of the above effect, the reflected light 600 from thereflection type liquid crystal panel 360 is diffused likewise inconsequence of the diffuse treatment, with bringing about an issue thatdisplayed characters are blurred in outline and deteriorated invisibility. Therefore, the haze value of the diffuse treatment to thelower face 332 of the light guide member or the surface of the substrate361 is preferably set to be 20% or lower. Results of experiments frommany people including women and old people show that the haze value isparticularly preferably 4-10% to keep an even balance between thereduction of bright lines by the reflected light 320 or 610 and theoutline blurring.

[0317] In the case where the lower face 332 of the light guide memberand the surface of the substrate 361 are both subjected to the diffusetreatment, the haze value of the diffuse treatment to the surface of thesubstrate 361 which is closer to the reflection type liquid crystalpanel 360 is set larger than that to the lower face 332 of the lightguide member separated farther from the liquid crystal panel 360, sothat the visibility is controlled not to decrease, in other words,displayed characters are prevented from blurring in outline, etc.

[0318] The visibility can be improved much more if both theanti-reflection treatment and the diffuse treatment are carried out tothe lower face 332 of the light guide member or the surface of thesubstrate 361.

[0319] Besides, when the anti-reflection film is formed on the upperface 331 of the light guide member 303, the reflection because of theexternal light can be lessened and the visibility can be improved.

[0320] A reflection type liquid crystal display device according to aneighth embodiment of the present invention will be discussed withreference to FIG. 39.

[0321] Parts in FIG. 39 indicated by the same reference numerals as inFIG. 38 are the same parts. 380 is a touch panel used, for example, forinputting of information through touching via a pen or finger, etc. Afront face 381 or a rear face 382 of the touch panel is processedthrough the diffuse treatment, thus diffusing the reflected light 320from the lower face 332 of the light guide member and the reflectedlight 610 from the surface of the substrate 361. The amount of lightsensed by human eyes as bright lines is decreased and the visibility canbe improved. In this arrangement alike, the haze value at the diffusetreatment is preferred to be set at 20% or lower in order to prevent theoutline blurring of displayed characters. Especially when the touchpanel is provided for the purpose of inputting information via a pen andif the haze value of the diffuse treatment to the front face 381 islarger than 10%, a write resistance is too large for the pen to runsmoothly. On the other hand, if the haze value is smaller than 1%, theresistance is too small. As such, the haze value for the front face 381is preferably 1-10%.

[0322] According to the display devices of the above-described seventhand eighth embodiments of the present invention, a transparent materialis filled between the lower face 332 of the light guide member 303 andthe reflection type liquid crystal panel 360 in the liquid crystaldisplay device, which has approximately the same refractive index asthat of a material of the light guide member 303 and that of thesubstrate 361 of the reflection type liquid crystal panel 360.Alternatively, a sheet of the above transparent material is interposed.The total quantity of the reflected light 320 and reflected light 610 isfurther decreased to the reflected light 600 from the liquid crystalpanel 360. The visibility can accordingly be improved more.

[0323] A method for manufacturing the illuminating system according to aseventh embodiment of the present invention will be depicted withreference to FIGS. 40, 41.

[0324] The anti-reflection treatment is primarily carried out by one ofthree methods, namely, vacuum vapor deposition, spin coating and dipcoating. Among the methods for the anti-reflection treatment, the dipcoating is preferred to the light guide member 303, because the spincoating is difficult if the light guide member 303 includes grooves 304and the vacuum vapor deposition method costs high. CYTOP by Asahi Glass,Co., Ltd. is employed by way of example as an anti-reflection agent inthe dip coating.

[0325] The light guide member 303 is used as a front face of the displaydevice, and therefore a uniform coat all over the face of the lightguide member 303 is required. A drop of the agent liquid from an endface of the light guide member 303 can be eliminated if the light guidemember 303 is inclined slantwise during the dip coating, as shown inFIG. 40. If the end face of the light guide member 303 is set inparallel to the liquid level without being inclined, the antireflectionagent accumulated at the end face of the light guide member 303 dropsafter the dipping, resulting in an irregular coat to the light guidemember 303.

[0326] In the case where the light guide member 303 is one formed byinjection molding, the anti-reflection coating can be obtained all overthe face of the light guide member 303 by holding a gate part 334 asillustrated in FIG. 40. In the absence of the gate part 334, the endface of the light guide member 303 is pressed from sideways to adirection of arrows as shown in FIG. 41, whereby the light guide memberis fixed to an outer frame 341.

[0327] In the above-described manner, the anti-reflection coating can beformed uniformly all over the face of the light guide member 303 at lowcost.

[0328] Although an inclination 0 of the light guide member 303 ispreferred to be large in order to prevent the agent from dropping, thelarger the inclination θ is, the thicker the coating becomes at thegrooves 304 of the upper face 331 than at the other parts. Therefore,the inclination is set as small as possible. The present invention foundfrom repeated experiments that the inclination θ of 10°-30° surelypresents the dropping of the agent and makes the thickness of thecoating at the grooves 304 of the upper face 331 equal to that at theother parts. The anti-reflection coating agent in this case has aviscosity of approximately 10 cps and a pull-up speed of 80 mm/min.

[0329] The above range of the inclination θ differs depending on theviscosity and pull-up speed of the anti-reflection coating agent.

[0330] A reflection type liquid crystal display device in a ninthembodiment of the present invention using the light guide member will bedescribed with reference to FIGS. 42, 43.

[0331]FIG. 42 is a schematically sectional view of the reflection typeliquid crystal display device according to the ninth embodiment which isequipped with the illuminating system.

[0332] The display device of the ninth embodiment is almost the same instructure as the eighth embodiment. A difference is an angle of thelight projected from the light guide member 303 and the presence of anfield angle control sheet 307 disposed on the reflection type liquidcrystal panel. In the ninth embodiment, the anti-reflection treatmentand the diffuse treatment are not required to the light guide member andthe reflection type liquid crystal panel.

[0333] The field angle control sheet 307 is a sheet which has a functionto diffuse light from one direction and pass light from the otherdirections, for instance, “Lumisty” by Sumitomo Chemical Company,Limited, “Lower” by Minnesota Mining and Manufacturing Company etc. Adiffusion direction θ of the field angle control sheet is not smallerthan an angle of field to a normal direction of the display device, forexample, 30° in the ninth embodiment.

[0334]FIG. 43 is an explanatory diagram of the propagation of light inthe ninth embodiment.

[0335] Supposing that an output angle of the light guide member 303 is30°, the unrequested reflected light 320 and also the unrequestedreflected light 610 are directed outside the angle of visibility (fieldangle). Since the light projected from the light guide member 303 isturned to diffused light when passing through the control sheet 307, thelight can illuminate the liquid crystal panel 306. Moreover, theoriginally necessary light reflected at the liquid crystal panel 306 isnot diffused by the field angle control sheet 307. Therefore, blurringof characters does not take place and superior visibility is achieved.

[0336] Although the diffusion direction θ is set to be 30° in the ninthembodiment, the angle θ may be a different value other than 30°.However, if the angle θ is small, the unnecessary reflected lights 320and 610 are projected into the angle of visibility, narrowing aneasy-to-see angle of the display device. If the angle θ is large, theluminance in the normal direction of the display device is decreased.After conducting experiments by changing the angle θ from 0° to 70°, theinventors detected that the easy-to-see angle is satisfied and theluminance in a direction of the front face is appropriate particularlywhen the angle is 30°-50°.

[0337] According to the light guide member of the seventh embodiment ofthe present invention as described hereinabove, the lower face of thelight guide member is processed through the anti-reflection treatment ordiffuse treatment, so that the total quantity of the reflected lightfrom the lower face of the light guide member is greatly reduced,specifically as much as is negligible enough to the reflected light fromthe reflecting face. The visibility can accordingly be improved large.

[0338] In the reflection type liquid crystal display device of theseventh embodiment using the light guide member, the reflection typeliquid crystal panel is provided which has the surface of at least onesubstrate processed through the anti-reflection treatment or diffusetreatment. Moreover, the liquid crystal panel is disposed so that thesurface subjected to at least one of the anti-reflection treatment andthe diffuse treatment confronts the lower face of the light guidemember. Accordingly, the reflected light from the lower face of thelight guide member is reduced as much as is negligible in comparisonwith the reflected light from the surface of the liquid crystal panel,and the visibility can be improved greatly.

[0339] The touch panel processed through the anti-reflection treatmentor diffuse treatment is arranged on the light guide member, therebyeasing bright lines of the reflected light from the lower face of thelight guide member and the surface of the substrate of the liquidcrystal panel and improving the visibility eventually.

[0340] The haze value of the diffuse treatment to the surface of thesubstrate of the reflection type liquid crystal panel is set larger thanthat of the diffuse treatment to the lower face of the light guidemember. Decrease in visibility such as outline blurring of displayedcharacters or the like can be hence restricted.

[0341] In the reflection type liquid crystal display device according tothe eighth embodiment of the present invention using the light guidemember, the transparent material of approximately the same refractiveindex as that of the material of the light guide member and that of thesubstrate of the reflection type liquid crystal panel is filled into, ora sheet of the material is interposed between the lower face of thelight guide member and the reflection type liquid crystal panel.Accordingly, the reflected light from the lower face of the light guidemember and from the surface of the substrate of the reflection typeliquid crystal panel is reduced to such a degree negligible as comparedwith the reflected light from the reflecting face of the liquid crystalpanel, so that the visibility can greatly be improved.

[0342] According to the method for manufacturing the light guide memberof the seventh embodiment, no drop of liquid is brought about from theend face of the light guide member. The anti-reflection treatment can beprovided uniformly to the whole face of the light guide member.

[0343] The anti-reflection treatment can be carried out simply byholding the gate part of the light guide member.

[0344] According to the reflection type liquid crystal display device ofthe ninth embodiment using the light guide member, the field anglecontrol plate (sheet) is arranged on the upper face of the reflectiontype liquid crystal panel. Since the angle of the illumination lightprojected from the lower face of the light guide member is nearly agreedwith the diffusion direction of the field angle control plate, the lightprojected from the lower face of the light guide member is diffused,whereas the reflected light from the reflection type liquid crystalpanel is not diffused, whereby the visibility can be improved.

[0345] Further, when each of the output angle of the light guide memberand diffusion direction of the field angle control plate is 30°-50° tothe normal direction of the liquid crystal panel, the reflected lightfrom the lower face of the light guide member and from the substrate ofthe liquid crystal panel are sent outside the angle of visibility, sothat the visibility can be improved.

[0346] The present invention can provide the light guide member easy tosee, the reflection type liquid crystal display device using the lightguide member and the manufacture method for the same.

[0347] Next, a tenth embodiment of the present invention will bedescribed.

[0348] A back light is used by way of example as an illuminating systemfor a liquid crystal panel. The back light is, as is disclosed inJapanese Laid-Open Patent Publication No. 5-127159, constituted of afluorescent lamp and a light guide member of a transparent flat plate,in which linear light from the fluorescent lamp is inputted to a sideface of the light guide member and output as a linear light source to aliquid crystal panel with the utilization of the diffusion of light atsilk printing provided at a rear face of the light guide member.

[0349] Lately, an illuminating system for illuminating the liquidcrystal panel used in a portable information-processing device, consumessmall power and operates at low voltage is required to achieve acompact, battery-driven structure with a long life. When the fluorescentlamp is used as the light source as in the above-mentioned back light, ahigh voltage generation circuit is necessitated to turn on thefluorescent lamp, and consequently, a loss at an electric circuit and aspace for the electric circuit are to be taken into consideration. Thelight source using the fluorescent lamp is not fit to carry with.

[0350] On the other hand, a light-emitting diode which will be referredto as an “LED” hereinafter is the light source that can be driven by abattery. Many LEDs are arranged into an array and used as the linearlight source to bring the light from the side face of the light guidemember.

[0351] In the arrangement of LEDs as above, however, an intensity oflight among the LEDs is decreased unless the LEDs are densely installed,varying a luminance distribution at the back light. Meanwhile, if theLEDs are arranged densely so as to eliminate the variation in luminancedistribution, a count of LEDs used is increased, with hindering a costreduction.

[0352] The tenth embodiment of the present invention provides a uniformlinear light source, with solving the above-discussed inconveniences.

[0353] The linear light source according to the tenth embodiment of thepresent invention will be described with reference to FIGS. 44-49.

[0354]FIGS. 44, 46 are diagrams of the linear light source in the tenthembodiment. In FIGS. 44 and 46, 801 is a light source of a smalllight-emitting part, for instance, an LED or the like. The light sources801 are arranged via a constant interval p. 805 is a diffusing plate.802 is a reflecting plate disposed to cover the light sources 801 anddiffusing plate 805. An inner face of the reflecting plate 802 isvapor-deposited with silver or aluminum, etc. to increase a reflectance.803 is a light guide plate serving as one example of the light guidemember, having the reflecting plate 802 set at a side face thereof toproject light entering from the side face to an upper face or a lowerface. 804 is the groove, 849 is an anti-reflection coating layer at thelower surface of the light guide plate 803. 851 is a liquid crystalpanel, 850 is an anti-reflection and anti-plate coating layer at theupper surface of the panel 850. 870 is a circuit board on which the LEDs801 are mounted. 880 is the touch panel of the eighth embodiment.

[0355] Supposing that a radial distribution of the light sources 801 isf(θ) and a distance between the light source 801 and diffusing plate 805is L, the following expression is held;

L>p/(2 tan(θ))

[0356] wherein θ is a value satisfying f(θ)cos²(θ)=0.5.

[0357] The linear light source 801 constituted as above achieves auniform illumination, the reason for which will be discussed withreference to FIGS. 48 and 49. FIGS. 48 and 49 are XZ sectional views ofthe linear light source 801. The light sources 801 are arranged in an Xdirection via the constant interval p and separated from the diffusingplate 805 by the distance L. One light-emitting point of the lightsources 801 is a point R, and an intersection of a line extending in adirection vertical to the point R, namely, in a Z direction and thediffusing plate 805 is a point Q. An intersection between a bisector ofthe point R and a light-emitting point R₁ next to the point R, and thediffusing plate 805 is a point P₁. A luminance in a direction inclinedby θ in the Z direction at the point R is f(θ) where (f(0)=1).

[0358] In order to make the light quantity from the light sources 801uniform at the diffusing plate 805, although it is enough tosufficiently separate the light sources 801 from the diffusing plate805, this makes the light source part bulky in size. For eliminating theproblem, therefore, a minimum distance between the light sources 801 anddiffusing plate 805 is calculated. Where the light quantity is smallestat the diffusing plate 805 is in the middle of light-emitting points Rand R₁ of the light sources 801, i.e., point P₁. The distance L isselected so that the light quantity at the point P₁ becomes equal tothat at the point Q, whereby the uniform linear light source isobtained.

[0359] The light reaching the point Q is mostly from the point R₁ andtherefore the light quantity at the point Q is 1/L². The quantity oflight reaching the point P₁ is 2f(θ)cos² θ/L². The θ is accordingly setto satisfy f(θ)cos² θ=0.5. Thus, the distance L between the lightsources 801 and diffusing plate 805 is determined to hold;

L>p/(2 tan(θ))

[0360] For example, when the radial distribution f(θ) of thelight-emitting points of the light sources 801 is equal to cos(θ), θ is37.5° because cos³ θ=0.5, and the distance L of the light source 801 anddiffusing plate 805 becomes L>0.65p.

[0361] As described hereinabove, when the light-emitting points of thelight sources 801 are arranged via the pitch p and if the light sources801 are separated from the diffusing plate 805 at least by L>p(2 tan(θ))wherein f(θ) is the radial distribution of the light-emitting points andf(θ)cos² θ is equal to 0.5, the uniform linear light source is realized.Since the LED or the like light source that can be driven at low voltageis utilizable, the illumination is achieved in a compact and low-powerstructure to fit for use in a portable information device, etc.

[0362] According to the tenth embodiment of the present invention, thediffusing plate and the prism sheet of the light guide member areseparated from the light sources by the distance L (L>p/(2 tan(θ))wherein f(θ) is the radial distribution of light-emitting points andf(θ)cos² θ is equal to 0.5. Accordingly, the linear illuminationprovided exerts high and uniform luminance.

[0363] The entire disclosure of Japanese Patent Applications No.9-122343 filed on May 13, 1997, No. 9-124992 filed on Aug. 21, 1997, andNo. 10-44960 filed on Feb. 26, 1998, including specifications, claims,drawings, and summaries are incorporated herein by reference in theirentirety.

[0364] Although the present invention has been fully described inconnection with the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. An illuminating system comprising a light source;and a transparent plate with the light source placed beside a side facethereof, wherein a plurality of grooves filled with a layer having arefractive index different from a refractive index of the transparentplate are arranged at specified intervals in a surface or interior ofthe transparent plate.
 2. An illuminating system according to claim 1 ,wherein a top face and a bottom face of the transparent plate aregenerally parallel to each other.
 3. An illuminating system according toclaim 1 , wherein a condition of θ<sin⁻¹(n ₁ /n)−sin⁻¹{(1/n)sin(β)} issatisfied where n is the refractive index of the transparent plate, n₁is the refractive index of a material as the layer that fills thegrooves which are the slits, θ is an angle formed by each of the slitsand the top face of the transparent plate and β is an angle ofvisibility of the illuminating system.
 4. An illuminating systemcomprising: a light source; a transparent first plate with the lightsource placed beside a side face thereof; and a transparent second plateplaced on a top face of the first plate, wherein a bottom face of thefirst plate is a plane surface and a plurality of stepwise slopes arearranged at specified intervals in the top face of the first plate; in abottom face of the second plate, stepwise slopes are arranged so as tobe identical in configuration to the slopes of the top face of the firstplate; and the top face of the first plate and the bottom face of thesecond plate are placed with a specified spacing.
 5. An illuminatingsystem according to claim 4 , wherein a condition of θ<sin⁻¹(n ₂/n)−sin⁻¹{(1/n)sin(β)} is satisfied where n is the refractive index ofthe first plate, n₂ is the refractive index of a material as the layerbonding the first plate and the second plate to each other, θ is anangle of each of the slopes of the top face of the first plate and thebottom face of the second plate and β is an angle of visibility of theilluminating system.
 6. An illuminating system according to claim 5 ,wherein a light outgoing angle of a collimator placed at an outgoingexit of the light source is within ±sin⁻¹[n×sin{90−θ−sin⁻¹(n₂/n)}]. 7.An illuminating system by overhead irradiation comprising: a lightsource; a transparent plate which is a light guide member in which aplurality of grooves are arranged in a top face of the light guidemember at specified intervals in a direction parallel to a longitudinaldirection of the light source, and in which a flat portion constitutinga part of the top face is arranged between adjacent ones of the grooves,wherein an illumination object placed on a bottom face side of the lightguide member is observed from a top face side of the light guide member.8. An illuminating system by overhead irradiation according to claim 7 ,wherein each of the grooves of the light guide member is a V-shapedgroove having a first slope located on one side closer to the lightsource and a second slope located on the other side farther from thelight source, and wherein an angle θ₁ formed by the first slope and thebottom face of the light guide member falls within a range ofθ₁≦90°−θ_(c)+2θ₃, where θ_(c) is a total reflection angle of the lightguide member and θ₃ is an angle formed by the flat portion and thebottom face of the light guide member.
 9. An illuminating system byoverhead irradiation according to claim 7 , wherein each of the groovesof the light guide member is a V-shaped groove having a first slopelocated on one side closer to the light source and a second slopelocated on the other side farther from the light source, and wherein anangle θ₁ formed by the first slope and the bottom face of the lightguide member satisfies a condition of: θ₁≈45+θ₃−(½)sin⁻¹(1/n×sinβ),where n is a refractive index of the light guide member, θ₃ is an angleformed by the flat portion and the bottom face of the light guide memberand β is an angle formed by a perpendicular of the bottom face of thelight guide member and a direction of the observer.
 10. An illuminatingsystem by overhead irradiation according to claim 7 , wherein each ofthe grooves of the light guide member is a V-shaped groove having afirst slope located on one side closer to the light source and a secondslope located on the other side farther from the light source, andwherein an angle θ₂ formed by the second slope and the bottom face ofthe light guide member satisfies a condition of θ₂≦(½)sin⁻¹(1/n), wheren is a refractive index of the light guide member.
 11. An illuminatingsystem by overhead irradiation according to claim 7 , wherein in thelight guide member, a pitch of the grooves is not more than a dot pitchof the illumination object.
 12. An illuminating system by overheadirradiation according to claim 7 , wherein each of the grooves of thelight guide member is a V-shaped groove having a first slope located onone side closer to the light source and a second slope located on theother side farther from the light source, and wherein in the light guidemember, a length of the first slope is not more than{L×(0.5/60)×_(π)/180}, where L is a distance between the top face of thelight guide member and an observer observing the illumination object.13. An illuminating system by overhead irradiation according to claim 7, wherein a transparent prism sheet is placed on the top face of thelight guide member, the prism sheet having, with respect to across-sectional shape, a plurality of projected portions having slopesof an angle θ₄ to the top face are arranged on the bottom face so that aflat portion generally parallel to the bottom face is interposedtherebetween.
 14. An illuminating system by overhead irradiationaccording to claim 13 , wherein the length of the slope of the prismsheet is not more than {L×(0.5/60)×_(π)/180}, where L is the distancebetween the observer who observes the illumination object and the topface of the light guide member.
 15. An illuminating system comprising: alight source; and a transparent plate taking light from the light sourcethrough a side face thereof and projecting illumination light through alower face thereof subjected to at least one of an anti-reflectiontreatment and a diffuse treatment, wherein an illumination object whichis disposed at a lower face side of the transparent plate is observedfrom an upper face side of the transparent plate.
 16. A reflection typeliquid crystal display device which comprises: the illuminating systemaccording to claim 1 , the transparent plate taking light from the lightsource through a side face thereof and projecting illumination lightthrough a lower face thereof subjected to at least one of ananti-reflection treatment and a diffuse treatment; and a reflection typeliquid crystal panel having a surface of at least one substrate thereofprocessed through at least one of the anti-reflection treatment and thediffuse treatment, wherein the surface of the substrate of the liquidcrystal panel processed through at least one of the anti-reflectiontreatment and the diffuse treatment is arranged to confront a lower faceof the transparent plate, so that the reflection type liquid crystalpanel is observed from an upper face side of the transparent plate. 17.A reflection type liquid crystal display device which comprises: theilluminating system according to claim 1 , the transparent plate takinglight from the light source through a side face thereof and projectingillumination light through a lower face thereof subjected to at leastone of an anti-reflection treatment and a diffuse treatment; areflection type liquid crystal panel having a surface of at least onesubstrate thereof processed through at least either an anti-reflectiontreatment or a diffuse treatment; and a touch panel having a surfaceprocessed through a diffuse treatment, wherein the surface of thesubstrate of the liquid crystal panel processed through at least eitherthe anti-reflection treatment or the diffuse treatment is arranged toconfront the lower face of the transparent plate and at the same time,the touch panel is disposed to confront an upper face of the transparentplate, so that the reflection type liquid crystal panel is observed froman upper face side of the transparent plate.
 18. A reflection typeliquid crystal display device according to claim 16 , wherein a hazevalue of the diffuse treatment provided to the surface of the substrateof the reflection type liquid crystal panel, the lower face of thetransparent plate or the surface of the touch panel is set to be notlarger than 20%.
 19. A reflection type liquid crystal display deviceaccording to claim 16 , wherein a transparent material or a sheet of thematerial which has approximately the same refractive index as that of amaterial of the transparent plate and that of the substrate of thereflection type liquid crystal panel is interposed between the lowerface of the transparent plate and the reflection type liquid crystalpanel.
 20. A reflection type liquid crystal display device whichcomprises: the illuminating system according to claim 1 , thetransparent plate taking light from the light source through a side facethereof and projecting illumination light from a lower face thereof; anda reflection type liquid crystal panel having an field angle controlplate arranged on an upper face thereof, said control plate featuring adiffuse characteristic in one direction while being transparent in otherdirections, wherein the face of the reflection type liquid crystal panelwhere the field angle control plate is arranged is set to confront thelower face of the transparent plate, and moreover an angle of theillumination light projected from the lower face of the transparentplate is almost agreed with a diffusion direction of the field anglecontrol plate, so that the reflection type liquid crystal panel isobserved from an upper face side of the transparent plate.
 21. Areflection type liquid crystal display device according to claim 20 ,wherein an output angle of the transparent plate and the diffusiondirection of the field angle control plate is 30-50° to a normaldirection of the reflection type liquid crystal panel.
 22. Anilluminating system according to claim 1 , wherein the light house is agroup of point light sources in which point light sources are arrangedon an almost straight line via a constant interval to radiate in nearlythe same direction, the illuminating system further comprising: areflector having an opening part and disposed to cover the group ofpoint light sources; and a diffusing plate set at the opening part ofthe reflector, wherein the diffusing plate is separated from the groupof point light sources so that quantity of light from a center of anilluminance distribution by the point light source on the diffusingplate is nearly equal to that between centers of illuminancedistributions of the point light sources.
 23. An illuminating systemaccording to claim 22 , wherein the reflector is L-shaped so as not todirectly pass light emitted from the point light sources to thediffusing plate.
 24. An illuminating system according to claim 22 ,which further comprises a light guide member which outputs lightentering from a side face thereof after emitted from the diffusing platearranged at the opening part of the reflector of the linear lightsource, from a lower face side thereof by grooves formed in a lower faceor an upper face thereof.